Soft tissue depth-finding tool

ABSTRACT

Apparatus is provided that includes a tissue anchor, which (a) comprises a helical tissue-coupling element which has a distal tissue-penetrating tip at a distal end of the tissue anchor, and which is configured to be advanced into soft tissue, and (b) is shaped so as to define a longitudinal channel extending to the distal end of the helical tissue-coupling element. The apparatus further includes a depth-finding tool, which comprises a radiopaque bead that is axially moveable along the channel so as to serve as a marker indicating a depth of penetration of the tissue-coupling element into the soft tissue.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.14/759,768, filed Jul. 8, 2015, which is the US national state ofInternational Application PCT/IL2014/050027, filed Jan. 9, 2014, whichclaims from U.S. Provisional Application 61/750,427, filed Jan. 9, 2013,which is assigned to the assignee of the present application and isincorporated herein by reference.

FIELD OF THE APPLICATION

The present invention relates generally to tissue anchors, andspecifically to anchors for tissue anchors for implantation in softtissue, such as cardiac tissue.

BACKGROUND OF THE APPLICATION

Tissue anchors are used for anchoring elements, such as electrode leadsor sutures, to tissue, such as bone or soft tissue. Some tissue anchorsare shaped so as to define a shaft and screw thread therearound, whileother tissue anchors are shaped so as define a helical tissue-couplingelement without a shaft.

SUMMARY OF THE APPLICATION

Some applications of the present invention provide tissue anchors, eachof which comprises a generally helical tissue-coupling element and,typically, a proximal head. Typically, the helical tissue-couplingelement has a generally rectangular, e.g., square, cross section. Forsome applications, the helical tissue-coupling element has (a) a firstaxial thickness along a first axial portion of a shaftless helicalportion of the helical tissue-coupling element, and (b) a second axialthickness along a second axial portion of the shaftless helical portionmore distal than the first axial portion. The second axial thickness isgreater than the first axial thickness. The first and second axialthicknesses are measured along a longitudinal axis of the helicaltissue-coupling element. Alternatively or additionally, the helicaltissue-coupling element has (a) a first axial yield strength along thefirst axial portion, and (b) a second axial yield strength along thesecond axial portion (more distal than the first axial portion). Thesecond axial yield strength is greater than the first axial yieldstrength. Further alternatively or additionally, the helicaltissue-coupling element has (a) a first axial stiffness along the firstaxial portion, and (b) a second axial stiffness along the second axialportion (more distal than the first axial portion). The second axialstiffness is greater than the first axial stiffness.

One result of these differing thicknesses, yield strengths, and/or axialstiffnesses is that if excessive tension is applied to the proximalhead, such as by a flexible longitudinal member as described below, thehelical tissue-coupling element generally elongates along the firstaxial portion before along the second axial portion. The first axialportion thus serves as a mechanical fuse. Providing the first axialportion effective reduces the force on the main part of the anchor whichholds the anchor in place, thereby reducing or eliminating the danger ofunscrewing the anchor, breaking the anchor, or tearing the tissue, bothduring the implantation procedure and thereafter during long-termimplantation of the anchor. Alternatively or additionally, the physicianmay reduce or cease increasing the tension before the second axialportion elongates, thereby reducing the risk of the elongation causingdamage to the tissue in which the second axial portion is implanted, andthe risk that the tension will pull the anchor from the tissue. For someapplications, the physician senses elongation of the first axial portionin real time while applying the tension, such as by using imaging and/ortactile feedback. The first axial portion may undergo plasticdeformation when elongated. As a result, excess force applied to theanchor is absorbed by the first axial portion, instead of detaching theanchor from the tissue, or causing failure elsewhere on the anchor.

For some applications, the helical tissue-coupling element is shaped soas to define (a) a first surface along a first axial surfacecharacteristic portion of the shaftless helical portion of the helicaltissue-coupling element, which first surface has a first surfacecharacteristic, and (b) a second surface along a second axial surfacecharacteristic portion of the shaftless helical portion different fromthe first axial surface characteristic portion. The second surface has asecond surface characteristic that is configured to inhibit rotation ofthe helical tissue-coupling element to a greater extent than does thefirst surface characteristic. The first surface characteristic may, forexample, be a high level of smoothness.

For some applications, the helical tissue-coupling element is configuredto rotate in a first rotational direction when being advanced intotissue, and the second surface characteristic is configured to inhibitrotation of the helical tissue-coupling element in the first rotationaldirection to a lesser extent than in a second rotational directionopposite the first rotational direction. The second surface thus isconfigured to generally not inhibit the distal advancing (e.g.,screwing) of the helical tissue-coupling element into the tissue, and toinhibit the proximal removal (e.g., unscrewing) of the helicaltissue-coupling element from the tissue, thereby providing betteranchoring of the helical tissue-coupling element in the tissue.

For some applications, the second surface is sawtooth-shaped so as toprovide the second surface characteristic. Typically, thesawtooth-shaped second surface does not define any cutting surfaces.Alternatively or additionally, for some applications, the second surfacecharacteristic is surface roughness. For some applications, thesevarying surface characteristics are implemented in combination with thevarying axial thicknesses, yield strengths, and/or stiffnesses describedhereinabove.

For some applications, the helical tissue-coupling element includes ashaftless single-helix axial portion, and a shaftless double-helix axialportion joined to the single-helix axial portion at a junction along thehelical tissue-coupling element. The shaftless single-helix axialportion is shaped so as to define a single helical element. Theshaftless double-helix axial portion is shaped so as to define twohelical elements axially offset from each other. The shaftless single-and double-helix portions are thus arranged such that the shaftlesssingle-helix portion axially splits into the shaftless double-helixportion at the junction. Typically, the shaftless double-helix axialportion is proximal to the shaftless single-helix axial portion.

An axial yield strength of the shaftless single-helix axial portion istypically greater than an axial yield strength of the shaftlessdouble-helix axial portion. These differing axial yield strengths mayprovide the same benefit described above regarding the differing axialyield strengths of the first and second axial portions. In addition, forsome applications, the two helical elements of the shaftlessdouble-helix portion are rotationally offset from each other by between160 and 200 degrees, such as 180 degrees, which may cancel out or reduceany moments of force.

For some applications, along at least a shaftless helical portion of thehelical tissue-coupling element, an axial thickness of the helicaltissue-coupling element varies while a radial thickness of the helicaltissue-coupling element remains constant. The axial thickness ismeasured along the axis, and the radial thickness is measuredperpendicular to the axis.

In general, the tissue anchors described herein provide good tissueanchoring, typically for at least the 500,000 to 1 million cardiaccycles required before cardiac tissue growth firmly implants theanchors. The configurations of the tissue anchors reduce the likelihoodof the tissue anchors unscrewing, coming loose with a portion of thetissue, or mechanically breaking.

In some applications of the present invention, the tissue anchor furthercomprises a radiopaque bead shaped so as to define a hole therethrough.The helical tissue-coupling element passes through the hole of the bead,such that the bead is slidable along the helical tissue-couplingelement. The bead thus serves as a marker that indicates a depth ofpenetration of the tissue-coupling element into soft tissue, such ascardiac tissue.

When rotated, the helical tissue-coupling element penetrates and isadvanced into the tissue. The bead does not penetrate the tissue, andthus remains at a surface of the tissue, in contact therewith. As aresult, as the tissue-coupling element advances into the tissue, thebead remains stationary and slides along the tissue-coupling elementtoward the proximal end of the anchor (and toward the head). In otherwords, the proximal end of the anchor (and the head) move closer to thebead, as measured along the axis. Both the bead and more proximalportions of the anchor (such as the head) are viewed using imaging(e.g., fluoroscopy), and the distance between the bead and the proximalend of the anchor (e.g., the head) is estimated and monitored in realtime as the anchor is advanced into the tissue. When the bead reaches adesired distance from the head (such as reaches the head itself), thetissue-coupling element has been fully advanced, e.g., screwed, into andembedded in the tissue, and the physician thus ceases rotating theanchor.

Without using a technique such as this for visualizing the advancementof the anchor into the tissue, it is often difficult to ascertain whenthe tissue anchor has been fully embedded into the tissue, because thetissue is difficult to see in some images, such as fluoroscopic images.As a result, the tissue anchor may inadvertently be insufficientlyadvanced into the tissue, resulting in poor anchoring in the tissue, orover-advanced into the tissue, possible tearing or otherwise damagingthe tissue.

Some applications of the present invention provide a depth-finding tool,which comprises a shaft and a radiopaque bead shaped so as to define ahole therethrough. The shaft and bead are arranged such that the shaftpasses through the hole of the bead, such that the bead is slidablealong the shaft. The tissue anchor is shaped so as to define alongitudinal channel extending from a proximal end to a distal endthereof. The shaft of the depth-finding tool is removably positionedwithin the channel, typically coaxially with the longitudinal axis ofthe anchor. The bead is positioned within the distal portion of thechannel. The bead is typically initially positioned at or near thedistal end of the tissue anchor. For some applications, the helicaltissue-coupling element is shaped so as to define a distal stopper thatprevents the bead from advancing distally off of the shaft.

The bead serves as a marker that indicates a depth of penetration of thehelical tissue-coupling element into soft tissue, such as cardiactissue. When rotated, the helical tissue-coupling element penetrates andis advanced into the tissue. The bead does not penetrate the tissue, andthus remains at the surface of the tissue, in contact therewith. As aresult, as the tissue-coupling element advances into the tissue, thebead remains stationary, and moves toward the proximal end of the anchor(and toward the head). In other words, the proximal end of the anchor(and the head) move closer to the bead, as measured along the axis.

Both the bead and more proximal portions of the anchor (such as thehead) are viewed using imaging (e.g., fluoroscopy), and the distancebetween the bead and the proximal end of the anchor (e.g., the head) isestimated and monitored in real time as the anchor is advanced into thetissue. When the bead reaches a desired distance from the head (such asreaches the head itself), the tissue-coupling element has been fullyadvanced, e.g., screwed, into and embedded in the tissue, and thephysician thus ceases rotating the anchor. The physician proximallywithdraws the shaft from the channel, leaving the bead at the proximalend of an empty space defined by the helix; the helical tissue-couplingelement contains the bead.

Without using a technique such as this for visualizing the advancementof the anchor into the tissue, it is often difficult to ascertain whenthe tissue anchor has been fully embedded into the tissue, because thetissue is difficult to see in some images, such as fluoroscopic images.As a result, the tissue anchor may inadvertently be insufficientlyadvanced into the tissue, resulting in poor anchoring in the tissue, orover-advanced into the tissue, possible tearing or otherwise damagingthe tissue.

In some applications of the present invention, the tissue anchors andtools described herein are used for repairing a tricuspid valve usingtension. Typically, the techniques described herein for repairing thetricuspid valve facilitate reducing of tricuspid valve regurgitation byaltering the geometry of the tricuspid valve and/or by altering thegeometry of the wall of the right atrium of the heart of the patient. Insome applications of the present invention, techniques are provided toachieve bicuspidization of the tricuspid valve. For such applications,typically, the anterior leaflet and the septal leaflet are drawntogether to enhance coaptation. For some applications, a firsttissue-engaging element, which comprises one of the tissue anchorsdescribed herein, punctures a portion of cardiac tissue of the patientand is implanted at a first implantation site. A second tissue-engagingelement comprises a stent that is implanted at a second implantationsite in either the inferior or superior vena cava. A flexiblelongitudinal member is coupled between the first and the secondtissue-engaging elements and used to provide tension between theelements. For some applications, a plurality of first tissue-engagingelements are provided (such as two or three), which are implanted inrespective portions of cardiac tissue in a vicinity of the heart valve.

Some applications of the present invention provide a delivery system fordelivering the first tissue-engaging element. The first tissue-engagingelement may optionally comprise one of the tissue anchors describedherein. The delivery system comprises an anchor-deployment tube and aradiopaque marker, which is coupled to a distal end of theanchor-deployment tube, typically by flexible connecting element, suchas a spring, a braid, a mesh, or a cut tube. The radiopaque marker andflexible connecting element are initially arranged radially surroundingthe first tissue-engaging element, such that the radiopaque marker isaxially moveable along the first tissue-engaging element with respect tothe distal end of the anchor-deployment tube. The flexible connectingelement axially compresses as the marker moves toward the distal end ofthe anchor-deployment tube. The flexible connecting element biases themarker distally. The marker may have any appropriate shape, such as adisc.

As the physician begins to rotate the first tissue-engaging element intotissue at the first implantation site, the spring pushes the markerdistally against the surface of the tissue. The marker does notpenetrate the tissue, and thus remains at the surface of the tissue, incontact therewith. As a result, as the physician continues to rotate thefirst tissue-engaging element further into the tissue, the surface ofthe tissue holds the marker in place, bringing the marker closer to thedistal end of the anchor-deployment tube and closer to the head of thefirst tissue-engaging element.

Both the marker and more proximal portions of the anchor (such as thehead) are viewed using imaging (e.g., fluoroscopy), and the distancebetween the market and the proximal end of the anchor (e.g., the head)is estimated and monitored in real time as the anchor is advanced intothe tissue. When the marker reaches a desired distance from the head(such as reaches the head itself), the tissue-coupling element has beenfully advanced, e.g., screwed, into and embedded in the tissue, and thephysician thus ceases rotating the anchor.

There is therefore provided, in accordance with an application of thepresent invention, apparatus including a tissue anchor, which includes ahelical tissue-coupling element disposed about a longitudinal axisthereof and having a distal tissue-penetrating tip, wherein the helicaltissue-coupling element has:

-   -   a first axial thickness along a first axial portion of a        shaftless helical portion of the helical tissue-coupling        element, and    -   a second axial thickness along a second axial portion of the        shaftless helical portion more distal than the first axial        portion, which second axial thickness is greater than the first        axial thickness, the first and second axial thicknesses being        measured along the axis.

For some applications, the helical tissue-coupling element has:

-   -   a first axial yield strength along the first axial portion of        the helical tissue-coupling element,    -   a second axial yield strength along the second axial portion of        the helical tissue-coupling element, which second axial yield        strength is greater than the first axial yield strength, and    -   a third axial yield strength along the third axial portion,        which third axial yield strength is less than the second axial        yield strength.

Alternatively or additionally, for some applications:

-   -   the first and the second axial portions are shaftless helical        portions of the helical tissue-coupling elements, and    -   the helical tissue-coupling element has:    -   a first axial thickness along the first axial portion, and    -   a second axial thickness along the second axial portion, which        second axial thickness is greater than the first axial        thickness, the first and second axial thicknesses being measured        along the axis.

For some applications, the helical tissue-coupling element has a thirdaxial thickness along the third axial portion, which third axialthickness is less than the second axial thickness, the third axialthickness being measured along the axis.

For some applications, the helical tissue-coupling element has a thirdaxial thickness along a third axial portion more distal than the secondaxial portion, which third axial thickness is less than the second axialthickness, the third axial thickness being measured along the axis.

Alternatively or additionally, for some applications, the tissue anchoris shaped so as to define a head at a proximal end thereof, and theapparatus further includes a flexible longitudinal member, which iscoupled to the head.

For some applications:

-   -   the distal tissue-penetrating tip is at a distal end of the        tissue anchor, and the tissue anchor is shaped so as to define a        longitudinal channel extending from a proximal end of the anchor        to the distal end, and    -   the apparatus further includes a depth-finding tool, which        includes a radiopaque bead shaped so as to define a hole        therethrough, which bead is positioned within the channel, such        that the bead is slidable along the channel.

For some applications, the depth-finding tool further includes a shaftthat is removably positioned within the channel, such that the shaftpasses through the hole of the bead, and such that the bead is slidablealong the shaft and along the channel. For some applications, a distaltip of the shaft is sharp.

For some applications, the helical tissue-coupling element is shaped soas to define a distal stopper that prevents the radiopaque bead fromadvancing distally off of the shaft.

For any of the applications described above:

-   -   the tissue anchor may be shaped so as to define a head at the        proximal end thereof,    -   the helical tissue-coupling element may be shaped so as to        define and radially surround an empty space that extends along        at least 75% of an axial length of the helical tissue-coupling        element,    -   a distal portion of the channel may coincide with the empty        space,    -   a proximal portion of the channel may be defined by the head,    -   the distal portion of the channel may be wider than the proximal        portion of the channel, and    -   the bead may be positioned within the distal portion of the        channel, in the empty space.

For any of the applications described above, the depth-finding tool mayfurther include a wire, which is at least partially disposed within thechannel, and which couples the bead to the a proximal portion of thetissue anchor, thereby preventing the bead from exiting the distal endof the tissue anchor. For some applications, the wire is shaped as ahelical spring.

There is further provided, in accordance with an application of thepresent invention, apparatus including a tissue anchor, which includes ahelical tissue-coupling element disposed about a longitudinal axisthereof and having a distal tissue-penetrating tip, wherein the helicaltissue-coupling element has:

-   -   a first axial yield strength along a first axial portion of the        helical tissue-coupling element,    -   a second axial yield strength along a second axial portion of        the helical tissue-coupling element more distal than the first        axial portion, which second axial yield strength is greater than        the first axial yield strength, and    -   a third axial yield strength along a third axial portion more        distal than the second axial portion, which third axial yield        strength is less than the second axial yield strength.

For some applications, the tissue anchor is shaped so as to define ahead at a proximal end thereof, and the first axial portion extends tothe head.

Alternatively or additionally, for some applications, the tissue anchoris shaped so as to define a head at a proximal end thereof, and theapparatus further includes a flexible longitudinal member, which iscoupled to the head.

There is still further provided, in accordance with an application ofthe present invention, apparatus including a tissue anchor, whichincludes a helical tissue-coupling element disposed about a longitudinalaxis thereof and having a distal tissue-penetrating tip, wherein thehelical tissue-coupling element has:

-   -   a first axial stiffness along a first axial portion of the        helical tissue-coupling element,    -   a second axial stiffness along a second axial portion of the        helical tissue-coupling element more distal than the first axial        portion, which second axial stiffness is greater than the first        axial stiffness, and    -   a third axial stiffness along a third axial portion more distal        than the second axial portion, which third axial stiffness is        less than the second axial stiffness.

For some applications, the tissue anchor is shaped so as to define ahead at a proximal end thereof, and the first axial portion extends tothe head.

Alternatively or additionally, for some applications, the tissue anchoris shaped so as to define a head at a proximal end thereof, and theapparatus further includes a flexible longitudinal member, which iscoupled to the head.

There is additionally provided, in accordance with an application of thepresent invention, apparatus including a tissue anchor, which includes ahelical tissue-coupling element disposed about a longitudinal axisthereof and having a distal tissue-penetrating tip, wherein the helicaltissue-coupling element is configured to rotate in a first rotationaldirection when being advanced into tissue, and has:

-   -   a first surface along a first axial portion of a shaftless        helical portion of the helical tissue-coupling element, which        first surface has a first surface characteristic, and    -   a second surface along a second axial portion of the shaftless        helical portion different from the first axial portion, which        second surface has a second surface characteristic that is        configured to (a) inhibit rotation of the helical        tissue-coupling element to a greater extent than does the first        surface characteristic, and (b) inhibit rotation of the helical        tissue-coupling element in the first rotational direction to a        lesser extent than in a second rotational direction opposite the        first rotational direction,    -   wherein the first and the second surfaces face in a same spatial        direction.

For some applications, the second axial portion is more proximal thanthe first axial portion. Alternatively, the second axial portion is moredistal than the first axial portion.

For some applications, the tissue anchor is shaped so as to define ahead at a proximal end thereof, and the first axial portion extends tothe head.

For some applications, the spatial direction is proximal, and the firstand the second surfaces face proximally.

For some applications, the tissue anchor is shaped so as to define ahead at a proximal end thereof, and the apparatus further includes aflexible longitudinal member, which is coupled to the head.

For any of the applications described above, the helical tissue-couplingelement may have a third surface along a third axial portion of thehelical tissue-coupling element more distal than the second axialportion, which third surface has a third surface characteristic that isconfigured to inhibit the rotation of the helical tissue-couplingelement to a lesser extent than does the second surface characteristic,and the first, the second, and the third surfaces may face in the samespatial direction. For some applications, the first and third surfacecharacteristics are configured to inhibit the rotation of the helicaltissue-coupling element to a same extent.

For any of the applications described above, the second surface may besawtooth-shaped so as to provide the second surface characteristic. Forsome applications, the sawtooth-shaped second surface does not defineany cutting surfaces. For some applications, the spatial direction isproximal, and the first and the second surfaces face proximally.

For any of the applications described above, the second surfacecharacteristic may be surface roughness. For some applications, thespatial direction is proximal, and the first and the second surfacesface proximally.

For any of the applications described above, an axial length of thefirst axial portion may be at least 10% of an axial length of thehelical tissue-coupling element, and/or the axial length of the firstaxial portion may be no more than 30% of the axial length of the helicaltissue-coupling element.

There is yet additionally provided, in accordance with an application ofthe present invention, apparatus including a tissue anchor, whichincludes:

-   -   a radiopaque bead shaped so as to define a hole therethrough;        and    -   a helical tissue-coupling element, which includes a shaftless        helical portion that (a) is disposed about a longitudinal axis        thereof, (b) has a distal tissue-penetrating tip, and (c) has an        axial length of at least 3 mm, and    -   wherein the shaftless helical portion passes through the hole of        the bead, such that the bead is slidable along the shaftless        helical portion.

For some applications, the axial length is less than 10 mm.

For some applications, the shaftless helical portion extends along atleast 75% of the axial length of the helical tissue-coupling element.

For some applications, the tissue anchor is shaped so as to define ahead at a proximal end thereof, and the apparatus further includes aflexible longitudinal member, which is coupled to the head.

For any of the applications described above, the radiopaque bead mayinclude a plurality of radiopaque beads shaped so as to definerespective holes therethrough, and the helical tissue-coupling elementmay pass through the holes of the beads such that the beads are slidablealong the helical tissue-coupling element.

For some applications:

-   -   the helical tissue-coupling element is disposed about a        longitudinal axis thereof, and has: (a) a first surface along a        first axial portion of the shaftless helical portion, which        first surface has a first surface characteristic, and (b) a        second surface along a second axial portion of the shaftless        helical portion different from the first axial portion, which        second surface has a second surface characteristic that is        configured to inhibit rotation of the helical tissue-coupling        element to a greater extent than does the first surface        characteristic,    -   a first one of the beads is initially positioned distal to the        second axial portion, and    -   a second one of the beads is initially positioned proximal to        the second axial portion.

For some applications, the radiopaque beads include exactly tworadiopaque beads.

For any of the applications described above, the helical tissue-couplingelement may be disposed about a longitudinal axis thereof, and may have:(a) a first surface along a first axial portion of the shaftless helicalportion, which first surface has a first surface characteristic, and (b)a second surface along a second axial portion of the shaftless helicalportion different from the first axial portion, which second surface hasa second surface characteristic that is configured to inhibit rotationof the helical tissue-coupling element to a greater extent than does thefirst surface characteristic, and the bead may be initially positioneddistal to the second axial portion. For some applications, the helicaltissue-coupling element is configured to rotate in a first rotationaldirection when being advanced into tissue, and the second surfacecharacteristic is configured to inhibit rotation of the helicaltissue-coupling element in the first rotational direction to a lesserextent than in a second rotational direction opposite the firstrotational direction.

There is also provided, in accordance with an application of the presentinvention, apparatus including a tissue anchor, which includes a helicaltissue-coupling element, which is disposed about a longitudinal axisthereof, has a distal tissue-penetrating tip, and includes at least:

-   -   a shaftless single-helix axial portion, which is shaped so as to        define a single helical element, and    -   a shaftless double-helix axial portion joined to the shaftless        single-helix axial portion at a junction along the helical        tissue-coupling element.

For some applications, the helical tissue-coupling element has an axiallength of at least 3 mm, and the shaftless single- and double-helixportions collectively extend along at least 75% of the axial length ofthe helical tissue-coupling element.

For some applications, the shaftless double-helix portion is shaped soas to define two helical elements rotationally offset from each other bybetween 160 and 200 degrees.

For some applications, the tissue anchor is shaped so as to define ahead at a proximal end thereof, and the apparatus further includes aflexible longitudinal member, which is coupled to the head.

For some applications, the shaftless single-helix axial portion has asingle-helix axial thickness at a first location on the shaftlesssingle-helix axial portion at a distance of 250 microns from thejunction, the distance measured circumferentially around the helicaltissue-coupling element; the shaftless double-helix axial portion,including the two helical elements and the axial gap, has a double-helixaxial thickness at a second location on the shaftless double-helix axialportion at the distance from the junction, the single-helix anddouble-helix axial thicknesses being measured along the axis; and thedouble-helix axial thickness equals between 75% and 120% of thesingle-helix axial thickness.

For some applications, the shaftless double-helix portion is shaped soas to define two helical elements axially offset from each other,separated by an axial gap.

For any of the applications described above, an axial yield strength ofthe shaftless single-helix axial portion may be greater than an axialyield strength of the shaftless double-helix axial portion. For someapplications, the axial yield strength of the shaftless single-helixaxial portion is at least 120% of the axial yield strength of theshaftless double-helix axial portion.

For any of the applications described above, the shaftless double-helixaxial portion may be proximal to the shaftless single-helix axialportion. For some applications, the tissue anchor is shaped so as todefine a head at a proximal end thereof, and wherein the shaftlessdouble-helix axial portion extends to the head.

There is further provided, in accordance with an application of thepresent invention, apparatus including:

-   -   a tissue anchor, which (a) includes a helical tissue-coupling        element which has a distal tissue-penetrating tip at a distal        end of the tissue anchor, and (b) is shaped so as to define a        longitudinal channel extending from a proximal end of the anchor        to the distal end; and    -   a depth-finding tool, which includes a radiopaque bead shaped so        as to define a hole therethrough, which bead is positioned        within the channel, such that the bead is slidable along the        channel.

For some applications, the depth-finding tool further includes a shaftthat is removably positioned within the channel, such that the shaftpasses through the hole of the bead, and such that the bead is slidablealong the shaft and along the channel. For some applications, a distaltip of the shaft is sharp. For some applications, the helicaltissue-coupling element is shaped so as to define a distal stopper thatprevents the radiopaque bead from advancing distally off of the shaft.

For any of the applications described above:

-   -   the tissue anchor may be shaped so as to define a head at the        proximal end thereof,    -   the helical tissue-coupling element may be shaped so as to        define and radially surround an empty space that extends along        at least 75% of an axial length of the helical tissue-coupling        element,    -   a distal portion of the channel may coincide with the empty        space,    -   a proximal portion of the channel may be defined by the head,    -   the distal portion of the channel may be wider than the proximal        portion of the channel, and    -   the bead may be positioned within the distal portion of the        channel, in the empty space.

For any of the applications described above, the depth-finding tool mayfurther include a wire, which is at least partially disposed within thechannel, and which couples the bead to the a proximal portion of thetissue anchor, thereby preventing the bead from exiting the distal endof the tissue anchor. For some applications, the wire is shaped as ahelical spring.

There is still further provided, in accordance with an application ofthe present invention, apparatus including a tissue anchor, whichincludes a helical tissue-coupling element disposed about a longitudinalaxis thereof and having a distal tissue-penetrating tip, the helicaltissue-coupling element including a wire which (a) is shaped as a helix,(b) has a non-circular cross section, and (c) is twisted about itslongitudinal axis, so as to define a ridged surface.

For some applications, the wire is twisted about its longitudinal axisat between 1 and 5 twists per cm of a length the wire before it isshaped into the helix.

For some applications, the cross section is shaped as a polygon.

For some applications, the tissue anchor is shaped so as to define ahead at a proximal end thereof, and the apparatus further includes aflexible longitudinal member, which is coupled to the head.

For any of the applications described above, the helical tissue-couplingelement may have:

-   -   a first axial stiffness along a first axial portion of the        helical tissue-coupling element,    -   a second axial stiffness along a second axial portion of the        helical tissue-coupling element more distal than the first axial        portion, which second axial stiffness is greater than the first        axial stiffness, and    -   a third axial stiffness along a third axial portion more distal        than the second axial portion, which third axial stiffness is        less than the second axial stiffness.

For some applications, the tissue anchor is shaped so as to define ahead at a proximal end thereof, and the first axial portion extends tothe head.

There is additionally provided, in accordance with an application of thepresent invention, apparatus for use with a tissue anchor, the apparatusincluding a delivery system, which includes:

-   -   an anchor-deployment tube;    -   a flexible connecting element selected from the group consisting        of: a spring, a braid, a mesh, and a cut tube;    -   a radiopaque marker, which is coupled to a distal end of the        anchor-deployment tube by the flexible connecting element,    -   wherein the radiopaque marker and the flexible connecting        element are arranged radially surrounding the tissue anchor,        such that the radiopaque marker is axially moveable along the        tissue anchor with respect to the distal end, and    -   wherein the flexible connecting element is arranged so as to        axially compress as the marker moves toward the distal end.

For some applications, the radiopaque marker is shaped as a disc.

There is also provided, in accordance with an application of the presentinvention, a method including:

-   -   providing a tissue anchor, which includes a helical        tissue-coupling element disposed about a longitudinal axis        thereof and having a distal tissue-penetrating tip, wherein the        helical tissue-coupling element has (a) a first axial yield        strength along a first axial portion of the helical        tissue-coupling element, (b) a second axial yield strength along        a second axial portion of the helical tissue-coupling element        more distal than the first axial portion, which second axial        yield strength is greater than the first axial yield strength,        and (c) a third axial yield strength along a third axial portion        more distal than the second axial portion, which third axial        yield strength is less than the second axial yield strength; and    -   advancing the helical tissue-coupling element into soft tissue.

For some applications:

-   -   providing the tissue anchor includes providing the tissue anchor        in which the helical tissue-coupling element has (a) a first        axial yield strength along the first axial portion of the        helical tissue-coupling element, and (b) a second axial yield        strength along the second axial portion of the helical        tissue-coupling element, which second axial yield strength is        greater than the first axial yield strength, and    -   the method further includes:    -   applying tension to a proximal head of the tissue anchor; and    -   sensing elongation of the first axial portion while applying the        tension.

For some applications, providing the tissue anchor includes providingthe tissue anchor in which the helical tissue-coupling element has (a) afirst axial stiffness along the first axial portion of the helicaltissue-coupling element, (b) a second axial stiffness along the secondaxial portion of the helical tissue-coupling element, which second axialstiffness is greater than the first axial stiffness, and (c) a thirdaxial stiffness along the third axial portion, which third axialstiffness is less than the second axial stiffness.

For some applications, providing the tissue anchor includes providingthe tissue anchor in which (i) the first and the second axial portionsare shaftless helical portions of the helical tissue-coupling elements,and (ii) the helical tissue-coupling element has (a) a first axialthickness along the first axial portion, and (b) a second axialthickness along the second axial portion, which second axial thicknessis greater than the first axial thickness, the first and second axialthicknesses being measured along the axis. For some applications,providing the tissue anchor includes providing the tissue anchor inwhich the helical tissue-coupling element has a third axial thicknessalong the third axial portion, which third axial thickness is less thanthe second axial thickness, the third axial thickness being measuredalong the axis.

For some applications, the method further includes applying tension to aproximal head of the tissue anchor. For some applications, applying thetension includes sensing elongation of the first axial portion whileapplying the tension. For some applications, sensing the elongationincludes sensing the elongation using imaging. Alternatively oradditionally, sensing the elongation includes sensing the elongationusing tactile feedback. For some applications, applying the tensionincludes pulling on a flexible longitudinal member that is coupled tothe proximal head.

For some applications, advancing the helical tissue-coupling elementinto the soft tissue includes advancing the second and the third axialportions completely into the soft tissue, and leaving at least a portionof the first axial portion outside of the soft tissue. For someapplications, leaving the at least a portion of the first axial portionoutside of the soft tissue includes leaving the first axial portionentirely outside of the soft tissue.

For some applications, providing the tissue anchor includes providingthe tissue anchor shaped so as to define a head at a proximal endthereof, and the first axial portion extends to the head.

For some applications:

-   -   wherein providing the tissue anchor includes providing the        tissue anchor (a) in which the distal tissue-penetrating tip is        at a distal end of the tissue anchor, and (b) which is shaped so        as to define a longitudinal channel extending from a proximal        end of the anchor to the distal end,    -   wherein the method further includes providing a depth-finding        tool, which includes a radiopaque bead shaped so as to define a        hole therethrough, which bead is positioned within the channel,        such that the bead is slidable along the channel, and    -   wherein advancing the helical tissue-coupling element into the        soft tissue includes advancing the helical tissue-coupling        element into the soft tissue, such that the bead comes into        contact with and remains at a surface of the soft tissue.

For some applications, providing the depth-finding tool includesproviding the depth-finding tool further including a shaft that isremovably positioned within the channel, such that the shaft passesthrough the hole of the bead, and the bead is slidable along the shaftand along the channel. For some applications, the method furtherincludes proximally withdrawing the shaft from the channel, leaving thebead in the channel. For some applications, providing the depth-findingtool includes providing the depth-finding tool in which a distal tip ofthe shaft is sharp. For some applications, the method further includesadvancing the shaft into the soft tissue while advancing the helicaltissue-coupling element into the soft tissue. For some applications, themethod further includes, after fully advancing the helicaltissue-coupling element into the soft tissue, proximally withdrawing theshaft from the channel, leaving the bead in the channel.

For some applications, the method further includes, before advancing thehelical tissue-coupling element into the soft tissue, inserting thesharp distal tip of the shaft into the soft tissue slightly, in order toprevent sliding of the depth-finding tool and the anchor on a surface ofthe soft tissue before advancing the anchor into the tissue.

For some applications, the method further includes: viewing the bead anda proximal portion of the soft tissue anchor using imaging; andassessing a depth of penetration of the helical tissue-coupling elementinto the soft tissue by estimating a distance between the bead and theproximal portion of the tissue anchor.

For some applications, providing the depth-finding tool includesproviding the depth-finding tool further including a wire, which is atleast partially disposed within the channel, and which couples the beadto the a proximal portion of the tissue anchor, thereby preventing thebead from exiting the distal end of the tissue anchor. For someapplications, wherein providing the depth-finding tool includesproviding the depth-finding tool in which the wire is shaped as ahelical spring.

For some applications:

-   -   providing the tissue anchor includes providing the tissue anchor        in which:        -   the tissue anchor is shaped so as to define a head at the            proximal end thereof,        -   the helical tissue-coupling element is shaped so as to            define and radially surround an empty space that extends            along at least 75% of an axial length of the helical            tissue-coupling element,        -   a distal portion of the channel coincides with the empty            space,        -   a proximal portion of the channel is defined by the head,            and        -   the distal portion of the channel is wider than the proximal            portion of the channel, and    -   providing the depth-finding tool includes providing the        depth-finding tool in which the bead is positioned within the        distal portion of the channel, in the empty space.

There is further provided, in accordance with an inventive concept 1 ofthe present invention, a method comprising:

-   -   providing a tissue anchor, which includes a helical        tissue-coupling element disposed about a longitudinal axis        thereof and having a distal tissue-penetrating tip, wherein the        helical tissue-coupling element has (a) a first axial yield        strength along a first axial portion of the helical        tissue-coupling element, and (b) a second axial yield strength        along a second axial portion of the helical tissue-coupling        element more distal than the first axial portion, which second        axial yield strength is greater than the first axial yield        strength;    -   advancing the helical tissue-coupling element into soft tissue;    -   applying tension to a proximal head of the tissue anchor; and    -   sensing elongation of the first axial portion while applying the        tension.        Inventive concept 2. The method according to inventive concept        1, wherein sensing the elongation comprises sensing the        elongation using imaging.        Inventive concept 3. The method according to inventive concept        1, wherein sensing the elongation comprises sensing the        elongation using tactile feedback.        Inventive concept 4. The method according to inventive concept        1, wherein applying the tension comprises pulling on a flexible        longitudinal member that is coupled to the proximal head.        Inventive concept 5. The method according to inventive concept        1, wherein advancing the helical tissue-coupling element into        the soft tissue comprises advancing the second axial portion        completely into the soft tissue, and leaving at least a portion        of the first axial portion outside of the soft tissue.        Inventive concept 6. The method according to inventive concept        5, wherein leaving the at least a portion of the first axial        portion outside of the soft tissue comprises leaving the first        axial portion entirely outside of the soft tissue.        Inventive concept 7. The method according to inventive concept        1, wherein providing the tissue anchor comprises providing the        tissue anchor shaped so as to define a head at a proximal end        thereof, and wherein the first axial portion extends to the        head.

There is still further provided, in accordance with an inventive concept8 of the present invention, a method comprising:

-   -   providing a tissue anchor, which includes a helical        tissue-coupling element disposed about a longitudinal axis        thereof and having a distal tissue-penetrating tip, wherein the        helical tissue-coupling element has (a) a first axial stiffness        along a first axial portion of the helical tissue-coupling        element, (b) a second axial stiffness along a second axial        portion of the helical tissue-coupling element more distal than        the first axial portion, which second axial stiffness is greater        than the first axial stiffness, and (c) a third axial stiffness        along a third axial portion more distal than the second axial        portion, which third axial stiffness is less than the second        axial stiffness; and    -   advancing the helical tissue-coupling element into soft tissue.        Inventive concept 9. The method according to inventive concept        8, further comprising applying tension to a proximal head of the        tissue anchor.        Inventive concept 10. The method according to inventive concept        9, wherein applying the tension comprises sensing elongation of        the first axial portion while applying the tension.        Inventive concept 11. The method according to inventive concept        10, wherein sensing the elongation comprises sensing the        elongation using imaging.        Inventive concept 12. The method according to inventive concept        10, wherein sensing the elongation comprises sensing the        elongation using tactile feedback.        Inventive concept 13. The method according to inventive concept        9, wherein applying the tension comprises pulling on a flexible        longitudinal member that is coupled to the proximal head.        Inventive concept 14. The method according to inventive concept        8, wherein advancing the helical tissue-coupling element into        the soft tissue comprises advancing the second and the third        axial portions completely into the soft tissue, and leaving at        least a portion of the first axial portion outside of the soft        tissue.        Inventive concept 15. The method according to inventive concept        14, wherein leaving the at least a portion of the first axial        portion outside of the soft tissue comprises leaving the first        axial portion entirely outside of the soft tissue.        Inventive concept 16. The method according to inventive concept        8, wherein providing the tissue anchor comprises providing the        tissue anchor shaped so as to define a head at a proximal end        thereof, and wherein the first axial portion extends to the        head.

There is additionally provided, in accordance with an inventive concept17 of the present invention, a method comprising:

-   -   providing a tissue anchor, which (a) includes a helical        tissue-coupling element which has a distal tissue-penetrating        tip at a distal end of the tissue anchor, and (b) is shaped so        as to define a longitudinal channel extending from a proximal        end of the anchor to the distal end;    -   providing a depth-finding tool, which includes a radiopaque bead        shaped so as to define a hole therethrough, which bead is        positioned within the channel, such that the bead is slidable        along the channel; and    -   advancing the helical tissue-coupling element into soft tissue,        such that the bead comes into contact with and remains at a        surface of the soft tissue.        Inventive concept 18. The method according to inventive concept        17, wherein providing the depth-finding tool comprises providing        the depth-finding tool further including a shaft that is        removably positioned within the channel, such that the shaft        passes through the hole of the bead, and the bead is slidable        along the shaft and along the channel.        Inventive concept 19. The method according to inventive concept        18, further comprising proximally withdrawing the shaft from the        channel, leaving the bead in the channel.        Inventive concept 20. The method according to inventive concept        18, wherein providing the depth-finding tool comprises providing        the depth-finding tool in which a distal tip of the shaft is        sharp.        Inventive concept 21. The method according to inventive concept        20, further comprising advancing the shaft into the soft tissue        while advancing the helical tissue-coupling element into the        soft tissue.        Inventive concept 22. The method according to inventive concept        21, further comprising, after fully advancing the helical        tissue-coupling element into the soft tissue, proximally        withdrawing the shaft from the channel, leaving the bead in the        channel.        Inventive concept 23. The method according to inventive concept        20, further comprising, before advancing the helical        tissue-coupling element into the soft tissue, inserting the        sharp distal tip of the shaft into the soft tissue slightly, in        order to prevent sliding of the depth-finding tool and the        anchor on a surface of the soft tissue before advancing the        anchor into the tissue.        Inventive concept 24. The method according to inventive concept        17, further comprising:    -   viewing the bead and a proximal portion of the soft tissue        anchor using imaging; and    -   assessing a depth of penetration of the helical tissue-coupling        element into the soft tissue by estimating a distance between        the bead and the proximal portion of the tissue anchor.        Inventive concept 25. The method according to inventive concept        17, wherein providing the depth-finding tool comprises providing        the depth-finding tool further including a wire, which is at        least partially disposed within the channel, and which couples        the bead to the a proximal portion of the tissue anchor, thereby        preventing the bead from exiting the distal end of the tissue        anchor.        Inventive concept 26. The method according to inventive concept        25, wherein providing the depth-finding tool comprises providing        the depth-finding tool in which the wire is shaped as a helical        spring.        Inventive concept 27. The method according to inventive concept        17,    -   wherein providing the tissue anchor comprises providing the        tissue anchor in which:        -   the tissue anchor is shaped so as to define a head at the            proximal end thereof,        -   the helical tissue-coupling element is shaped so as to            define and radially surround an empty space that extends            along at least 75% of an axial length of the helical            tissue-coupling element,        -   a distal portion of the channel coincides with the empty            space,        -   a proximal portion of the channel is defined by the head,            and        -   the distal portion of the channel is wider than the proximal            portion of the channel, and    -   wherein providing the depth-finding tool comprises providing the        depth-finding tool in which the bead is positioned within the        distal portion of the channel, in the empty space.

There is yet additionally provided, in accordance with an inventiveconcept 28 of the present invention, a method comprising:

-   -   providing a tissue anchor, which includes a helical        tissue-coupling element disposed about a longitudinal axis        thereof and having a distal tissue-penetrating tip, wherein the        helical tissue-coupling element has (a) a first axial thickness        along a first axial portion of a shaftless helical portion of        the helical tissue-coupling element, and (b) a second axial        thickness along a second axial portion of the shaftless helical        portion more distal than the first axial portion, which second        axial thickness is greater than the first axial thickness, the        first and second axial thicknesses being measured along the        axis; and    -   advancing the helical tissue-coupling element into soft tissue.        Inventive concept 29. The method according to inventive concept        28, further comprising applying tension to a proximal head of        the tissue anchor.        Inventive concept 30. The method according to inventive concept        29, wherein applying the tension comprises sensing elongation of        the first axial portion while applying the tension.        Inventive concept 31. The method according to inventive concept        30, wherein sensing the elongation comprises sensing the        elongation using imaging.        Inventive concept 32. The method according to inventive concept        30, wherein sensing the elongation comprises sensing the        elongation using tactile feedback.        Inventive concept 33. The method according to inventive concept        29, wherein applying the tension comprises pulling on a flexible        longitudinal member that is coupled to the proximal head.        Inventive concept 34. The method according to inventive concept        28, wherein advancing the helical tissue-coupling element into        the soft tissue comprises advancing the second axial portion        completely into the soft tissue, and leaving at least a portion        of the first axial portion outside of the soft tissue.        Inventive concept 35. The method according to inventive concept        34, wherein leaving the at least a portion of the first axial        portion outside of the soft tissue comprises leaving the first        axial portion entirely outside of the soft tissue.        Inventive concept 36. The method according to inventive concept        28, wherein providing the tissue anchor comprises providing the        tissue anchor in which the helical tissue-coupling element has a        third axial thickness along a third axial portion more distal        than the second axial portion, which third axial thickness is        less than the second axial thickness, the third axial thickness        being measured along the axis.

There is also provided, in accordance with an inventive concept 37 ofthe present invention, a method comprising:

-   -   providing a tissue anchor, which includes a helical        tissue-coupling element disposed about a longitudinal axis        thereof and having a distal tissue-penetrating tip, wherein the        helical tissue-coupling element has (a) a first axial stiffness        along a first axial portion of the helical tissue-coupling        element, and (b) a second axial stiffness along a second axial        portion of the helical tissue-coupling element more distal than        the first axial portion, which second axial stiffness is greater        than the first axial stiffness;    -   advancing the helical tissue-coupling element into soft tissue;    -   applying tension to a proximal head of the tissue anchor; and    -   sensing elongation of the first axial portion while applying the        tension.        Inventive concept 38. The method according to inventive concept        37, wherein sensing the elongation comprises sensing the        elongation using imaging.        Inventive concept 39. The method according to inventive concept        37, wherein sensing the elongation comprises sensing the        elongation using tactile feedback.        Inventive concept 40. The method according to inventive concept        37, wherein applying the tension comprises pulling on a flexible        longitudinal member that is coupled to the proximal head.        Inventive concept 41. The method according to inventive concept        37, wherein advancing the helical tissue-coupling element into        the soft tissue comprises advancing the second axial portion        completely into the soft tissue, and leaving at least a portion        of the first axial portion outside of the soft tissue.        Inventive concept 42. The method according to inventive concept        41, wherein leaving the at least a portion of the first axial        portion outside of the soft tissue comprises leaving the first        axial portion entirely outside of the soft tissue.        Inventive concept 43. The method according to inventive concept        37, wherein providing the tissue anchor comprises providing the        tissue anchor shaped so as to define a head at a proximal end        thereof, and wherein the first axial portion extends to the        head.

There is further provided, in accordance with an inventive concept 44 ofthe present invention, a method comprising:

-   -   providing a tissue anchor, which includes a helical        tissue-coupling element disposed about a longitudinal axis        thereof and having a distal tissue-penetrating tip, wherein the        helical tissue-coupling element has (a) a first surface along a        first axial portion of a shaftless helical portion of the        helical tissue-coupling element, which first surface has a first        surface characteristic, and (b) a second surface along a second        axial portion of the shaftless helical portion different from        the first axial portion; and    -   advancing the helical tissue-coupling element into soft tissue,    -   wherein the second surface has a second surface characteristic        that is configured to, immediately upon advancing of the helical        tissue-coupling element into the soft tissue, mechanically        inhibit rotation of the helical tissue-coupling element to a        greater extent than does the first surface characteristic, and    -   wherein the first and the second surfaces face in a same spatial        direction.        Inventive concept 45. The method according to inventive concept        44, wherein advancing the helical tissue-coupling element into        the soft tissue comprises advancing the second axial portion        completely into the soft tissue.        Inventive concept 46. The method according to inventive concept        44, wherein providing the tissue anchor comprises providing the        tissue anchor in which the second axial portion is more proximal        than the first axial portion.        Inventive concept 47. The method according to inventive concept        44, wherein providing the tissue anchor comprises providing the        tissue anchor in which the second axial portion is more distal        than the first axial portion.        Inventive concept 48. The method according to inventive concept        47, wherein advancing the helical tissue-coupling element into        the soft tissue comprises advancing the second axial portion        completely into the soft tissue, and leaving at least a portion        of the first axial portion outside of the soft tissue.        Inventive concept 49. The method according to inventive concept        44, wherein providing the tissue anchor comprises providing the        tissue anchor in which the helical tissue-coupling element has a        third surface along a third axial portion of the helical        tissue-coupling element more distal than the second axial        portion, which third surface has a third surface characteristic        that is configured to inhibit the rotation of the helical        tissue-coupling element to a lesser extent than does the second        surface characteristic, and the first, the second, and the third        surfaces face in the same spatial direction.        Inventive concept 50. The method according to inventive concept        49, wherein providing the tissue anchor comprises providing the        tissue anchor in which the first and third surface        characteristics are configured to inhibit the rotation of the        helical tissue-coupling element to a same extent.        Inventive concept 51. The method according to inventive concept        44,    -   wherein advancing the helical tissue-coupling element into the        soft tissue comprises rotating the helical tissue-coupling        element in a first rotational direction, and    -   wherein providing the tissue anchor comprises providing the        tissue anchor in which the second surface characteristic is        configured to inhibit rotation of the helical tissue-coupling        element in the first rotational direction to a lesser extent        than in a second rotational direction opposite the first        rotational direction.        Inventive concept 52. The method according to inventive concept        44, wherein providing the tissue anchor comprises providing the        tissue anchor in which the tissue anchor is shaped so as to        define a head at a proximal end thereof, and wherein the first        axial portion extends to the head.        Inventive concept 53. The method according to inventive concept        44, wherein the spatial direction is proximal, and wherein        providing the tissue anchor comprises providing the tissue        anchor in which the first and the second surfaces face        proximally.        Inventive concept 54. The method according to inventive concept        44, wherein providing the tissue anchor comprises providing the        tissue anchor in which the second surface is sawtooth-shaped so        as to provide the second surface characteristic.        Inventive concept 55. The method according to inventive concept        54, wherein providing the tissue anchor comprises providing the        tissue anchor in which the sawtooth-shaped second surface does        not define any cutting surfaces.        Inventive concept 56. The method according to inventive concept        54, wherein the spatial direction is proximal, and wherein        providing the tissue anchor comprises providing the tissue        anchor in which the first and the second surfaces face        proximally.        Inventive concept 57. The method according to inventive concept        44, wherein the second surface characteristic is surface        roughness.        Inventive concept 58. The method according to inventive concept        57, wherein the spatial direction is proximal, and wherein        providing the tissue anchor comprises providing the tissue        anchor in which the first and the second surfaces face        proximally.

There is still further provided, in accordance with an inventive concept59 of the present invention, a method comprising:

-   -   providing a tissue anchor, which includes (a) a radiopaque bead        shaped so as to define a hole therethrough, and (b) a helical        tissue-coupling element, which includes a shaftless helical        portion that (i) is disposed about a longitudinal axis        thereof, (ii) has a distal tissue-penetrating tip, and (iii) has        an axial length of at least 3 mm, wherein the shaftless helical        portion passes through the hole of the bead, such that the bead        is slidable along the shaftless helical portion; and    -   advancing the helical tissue-coupling element into soft tissue,        such that the bead comes into contact with and remains at a        surface of the soft tissue.        Inventive concept 60. The method according to inventive concept        59, further comprising:    -   viewing the bead and a proximal portion of the soft tissue        anchor using imaging; and    -   assessing a depth of penetration of the helical tissue-coupling        element into the soft tissue by estimating a distance between        the bead and the proximal portion of the tissue anchor.        Inventive concept 61. The method according to inventive concept        59, wherein providing the tissue anchor comprises providing the        tissue anchor in which the radiopaque bead includes a plurality        of radiopaque beads shaped so as to define respective holes        therethrough, and the helical tissue-coupling element passes        through the holes of the beads such that the beads are slidable        along the helical tissue-coupling element.        Inventive concept 62. The method according to inventive concept        61,    -   wherein providing the tissue anchor comprises providing the        tissue anchor in which the helical tissue-coupling element is        disposed about a longitudinal axis thereof, and has (a) a first        surface along a first axial portion of the shaftless helical        portion, which first surface has a first surface characteristic,        and (b) a second surface along a second axial portion of the        shaftless helical portion different from the first axial        portion, which second surface has a second surface        characteristic that is configured to inhibit rotation of the        helical tissue-coupling element to a greater extent than does        the first surface characteristic, and    -   wherein advancing comprises beginning the advancing when a first        one of the beads is initially positioned distal to the second        axial portion, and a second one of the beads is initially        positioned proximal to the second axial portion.        Inventive concept 63. The method according to inventive concept        62, wherein advancing further comprises monitoring a position of        the first bead with respect to a distal end of the second axial        portion.        Inventive concept 64. The method according to inventive concept        63, wherein advancing further comprises:    -   ceasing the advancing when the first bead reaches the distal end        of the second axial portion;    -   thereafter, applying tension to a proximal head of the tissue        anchor, and assessing whether the tissue anchor is placed in an        appropriate location; and    -   thereafter, if the tissue anchor is placed in the appropriate        location:        -   continuing the advancing at least until a portion of the            second axial portion is within the soft tissue;        -   viewing the second bead and the proximal portion of the soft            tissue anchor using imaging; and        -   assessing a depth of penetration of the helical            tissue-coupling element into the soft tissue by estimating a            distance between the second bead and the proximal portion of            the tissue anchor.            Inventive concept 65. The method according to inventive            concept 61, wherein providing the tissue anchor comprises            providing the tissue anchor in which the radiopaque beads            include exactly two radiopaque beads.            Inventive concept 66. The method according to inventive            concept 59,    -   wherein providing the tissue anchor comprises providing the        tissue anchor in which the helical tissue-coupling element is        disposed about a longitudinal axis thereof, and has (a) a first        surface along a first axial portion of the shaftless helical        portion, which first surface has a first surface characteristic,        and (b) a second surface along a second axial portion of the        shaftless helical portion different from the first axial        portion, which second surface has a second surface        characteristic that is configured to inhibit rotation of the        helical tissue-coupling element to a greater extent than does        the first surface characteristic, and    -   wherein advancing comprises beginning the advancing when the        bead is initially positioned distal to the second axial portion.        Inventive concept 67. The method according to inventive concept        66, wherein advancing further comprises monitoring a position of        the bead with respect to a distal end of the second axial        portion.        Inventive concept 68. The method according to inventive concept        67, wherein advancing further comprises:    -   ceasing the advancing when the bead reaches the distal end of        the second axial portion;    -   thereafter, applying tension to a proximal head of the tissue        anchor, and assessing whether the tissue anchor is placed in an        appropriate location; and    -   thereafter, if the tissue anchor is placed in the appropriate        location, continuing the advancing at least until a portion of        the second axial portion is within the soft tissue.        Inventive concept 69. The method according to inventive concept        66, wherein providing the tissue anchor comprises providing the        tissue anchor in which the helical tissue-coupling element is        configured to rotate in a first rotational direction when being        advanced into tissue, and the second surface characteristic is        configured to inhibit rotation of the helical tissue-coupling        element in the first rotational direction to a lesser extent        than in a second rotational direction opposite the first        rotational direction.        Inventive concept 70. The method according to inventive concept        59, wherein providing the tissue anchor comprises providing the        tissue anchor in which the shaftless helical portion extends        along at least 75% of the axial length of the helical        tissue-coupling element.

There is additionally provided, in accordance with an inventive concept71 of the present invention, a method comprising:

-   -   providing a tissue anchor, which includes a helical        tissue-coupling element, which is disposed about a longitudinal        axis thereof, has a distal tissue-penetrating tip, and includes        at least (a) a shaftless single-helix axial portion, which is        shaped so as to define a single helical element, and (b) a        shaftless double-helix axial portion joined to the shaftless        single-helix axial portion at a junction along the helical        tissue-coupling element; and advancing the helical        tissue-coupling element into soft tissue.        Inventive concept 72. The method according to inventive concept        71, further comprising applying tension to a proximal head of        the tissue anchor.        Inventive concept 73. The method according to inventive concept        72,    -   wherein providing the tissue anchor comprises providing the        tissue anchor in which the shaftless double-helix axial portion        is proximal to the shaftless single-helix axial portion, and    -   wherein applying the tension comprises sensing elongation of the        shaftless double-helix axial portion while applying the tension.        Inventive concept 74. The method according to inventive concept        73, wherein sensing the elongation comprises sensing the        elongation using imaging.        Inventive concept 75. The method according to inventive concept        73, wherein sensing the elongation comprises sensing the        elongation using tactile feedback.        Inventive concept 76. The method according to inventive concept        73, wherein providing the tissue anchor comprises providing the        tissue anchor in which the shaftless double-helix axial portion        extends to the head.        Inventive concept 77. The method according to inventive concept        72, wherein applying the tension comprises pulling on a flexible        longitudinal member that is coupled to the proximal head.        Inventive concept 78. The method according to inventive concept        71, wherein advancing the helical tissue-coupling element into        the soft tissue comprises advancing the shaftless single-helix        axial portion completely into the soft tissue, and leaving at        least a portion of the shaftless double-helix axial portion        outside of the soft tissue.        Inventive concept 79. The method according to inventive concept        78, wherein leaving the at least a portion of the shaftless        double-helix axial portion outside of the soft tissue comprises        leaving the shaftless double-helix axial portion entirely        outside of the soft tissue.        Inventive concept 80. The method according to inventive concept        71, wherein providing the tissue anchor comprises providing the        tissue anchor in which an axial yield strength of the shaftless        single-helix axial portion is greater than an axial yield        strength of the shaftless double-helix axial portion.        Inventive concept 81. The method according to inventive concept        80, wherein providing the tissue anchor comprises providing the        tissue anchor in which the axial yield strength of the shaftless        single-helix axial portion is at least 120% of the axial yield        strength of the shaftless double-helix axial portion.        Inventive concept 82. The method according to inventive concept        71, wherein providing the tissue anchor comprises providing the        tissue anchor in which the shaftless double-helix portion is        shaped so as to define two helical elements axially offset from        each other, separated by an axial gap.        Inventive concept 83. The method according to inventive concept        71, providing the tissue anchor comprises providing the tissue        anchor in which:    -   the shaftless single-helix axial portion has a single-helix        axial thickness at a first location on the shaftless        single-helix axial portion at a distance of 250 microns from the        junction, the distance measured circumferentially around the        helical tissue-coupling element,    -   the shaftless double-helix axial portion, including the two        helical elements and the axial gap, has a double-helix axial        thickness at a second location on the shaftless double-helix        axial portion at the distance from the junction, the        single-helix and double-helix axial thicknesses being measured        along the axis, and    -   the double-helix axial thickness equals between 75% and 120% of        the single-helix axial thickness.        Inventive concept 84. The method according to inventive concept        71, wherein providing the tissue anchor comprises providing the        tissue anchor in which the helical tissue-coupling element has        an axial length of at least 3 mm, and wherein the shaftless        single-and double-helix portions collectively extend along at        least 75% of the axial length of the helical tissue-coupling        element.        Inventive concept 85. The method according to inventive concept        71, wherein providing the tissue anchor comprises providing the        tissue anchor in which the shaftless double-helix portion is        shaped so as to define two helical elements rotationally offset        from each other by between 160 and 200 degrees.

There is yet additionally provided, in accordance with an inventiveconcept 86 of the present invention, a method comprising:

-   -   providing a tissue anchor, which comprises a helical        tissue-coupling element disposed about a longitudinal axis        thereof and having a distal tissue-penetrating tip, the helical        tissue-coupling element comprising a wire which (a) is shaped as        a helix, (b) has a non-circular cross section, and (c) is        twisted about its longitudinal axis, so as to define a ridged        surface;    -   advancing the helical tissue-coupling element into soft tissue.        Inventive concept 87. The method according to inventive concept        86, wherein providing the tissue anchor comprises providing the        tissue anchor in which the cross section is shaped as a polygon.        Inventive concept 88. The method according to inventive concept        86, wherein providing the tissue anchor comprises providing the        tissue anchor in which the helical tissue-coupling element        has (a) a first axial stiffness along a first axial portion of        the helical tissue-coupling element, (b) a second axial        stiffness along a second axial portion of the helical        tissue-coupling element more distal than the first axial        portion, which second axial stiffness is greater than the first        axial stiffness, and (c) a third axial stiffness along a third        axial portion more distal than the second axial portion, which        third axial stiffness is less than the second axial stiffness.        Inventive concept 89. The method according to inventive concept        88, wherein providing the tissue anchor comprises providing the        tissue anchor in which the tissue anchor is shaped so as to        define a head at a proximal end thereof, and wherein the first        axial portion extends to the head.        Inventive concept 90. The method according to inventive concept        86, wherein providing the tissue anchor comprises providing the        tissue anchor in which the tissue anchor is shaped so as to        define a head at a proximal end thereof, and the method further        comprises a flexible longitudinal member, which is coupled to        the head.

There is also provided, in accordance with an inventive concept 91 ofthe present invention, a method comprising:

-   -   advancing a tissue anchor to soft tissue using an        anchor-deployment tube, a distal end of which anchor-deployment        tube is coupled to a radiopaque marker by a flexible connecting        element selected from the group consisting of: a spring, a        braid, a mesh, and a cut tube, such that the radiopaque marker        and the flexible connecting element are arranged radially        surrounding the tissue anchor, such that the radiopaque marker        is axially moveable along the tissue anchor with respect to the        distal end;    -   penetrating the tissue anchor into the soft tissue, such that        the flexible connecting element pushes the radiopaque marker        distally against a surface of the soft tissue; and    -   advancing the tissue anchor into the soft tissue, thereby moving        the radiopaque marker toward the distal end, such that the        flexible connecting element axially compresses.        Inventive concept 92. The method according to inventive concept        91, wherein the radiopaque marker is shaped as a disc.        Inventive concept 93. The method according to inventive concept        91, wherein the flexible connecting element comprises the        spring.        Inventive concept 94. The method according to inventive concept        91, wherein the flexible connecting element comprises the braid.        Inventive concept 95. The method according to inventive concept        91, further comprising:    -   viewing the radiopaque marker and a proximal portion of the        tissue anchor using imaging; and    -   assessing a depth of penetration of the tissue anchor into the        soft tissue by estimating a distance between the radiopaque        marker and the proximal portion of the tissue anchor.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-B are schematic illustrations of a tissue anchor, in accordancewith an application of the present invention;

FIGS. 2A-B are schematic illustrations of another tissue anchor, inaccordance with an application of the present invention;

FIGS. 3A-F are schematic illustrations of a tissue anchor and adepth-finding tool, in accordance with an application of the presentinvention;

FIGS. 4A-B are schematic illustrations of still another tissue anchor,in accordance with an application of the present invention;

FIGS. 5A-C and 6 are schematic illustrations of another tissue anchor atseveral stage of implantation in soft tissue, in accordance withrespective applications of the present invention;

FIGS. 7A-D are schematic illustrations of a system comprising a firsttissue-engaging element and a second tissue-engaging element forrepairing a tricuspid valve, in accordance with some applications of thepresent invention;

FIGS. 8A-C are schematic illustrations of yet another tissue anchor, inaccordance with respective applications of the present invention; and

FIGS. 9A-B and 10A-B are schematic illustrations of two configurationsof a delivery system, in accordance with respective applications of thepresent invention.

DETAILED DESCRIPTION OF APPLICATIONS

FIGS. 1A-B are schematic illustrations of a tissue anchor 20, inaccordance with an application of the present invention. FIG. 1A is anisometric view of the anchor, and FIG. 1B is a cross-sectional viewtaken along line IB-IB of FIG. 1A. Tissue anchor 20 comprises agenerally helical tissue-coupling element 30 disposed about alongitudinal axis 32 thereof and having a distal tissue-penetrating tip34 at a distal end 36 of tissue anchor 20. Typically, tissue anchor 20is shaped so as to define a head 40 at a proximal end 42 thereof.Typically, tissue-coupling element 30 has a generally rectangular, e.g.,square, cross section.

For some applications, along at least a shaftless helical portion 50 ofhelical tissue-coupling element 30, an axial thickness T_(A) of thehelical tissue-coupling element varies while a radial thickness T_(R) ofthe helical tissue-coupling element remains constant. Axial thicknessT_(A) is measured along axis 32, and radial thickness T_(R) is measuredperpendicular to the axis. (The radial thickness is sometimes referredto in the art as “wall thickness,” particularly for configurations inwhich the helical element is manufactured by cutting a tube, asdescribed hereinbelow. The axial thickness is sometimes referred to inthe art as “strut width.”)

Typically, radial thickness T_(R) of helical tissue-coupling element 30remains constant along at least 50% of an axial length L of the helicaltissue-coupling element, such as along 100% of axial length L.Typically, shaftless helical portion 50 extends between 50% and 100% ofaxial length L of helical tissue-coupling element 30 (In other words,shaftless helical portion 50 does not necessarily extend along theentire axial length L of the helical tissue-coupling element, as labeledin FIG. 1B, even in cases in which the helical tissue-coupling elementis shaftless along its entire length L. For example, the shaftlesshelical portion may extend along only a portion of the shaftless length,such as labeled 50′ in FIG. 1B.)

As used in the present application, including in the claims, “shaftless”means lacking a shaft (also sometimes known as a shank) that has anouter surface that is shaped so as to define the helix of helicaltissue-coupling element 30. For example, the helical thread of a screwis not shaftless, because the outer surface of the shaft of the screw isshaped so as to define the thread. It is noted that even if a shaft ofhead 40 extends into helical tissue-coupling element 30, the area intowhich the shaft of the head extends is still “shaftless” because theshaft of the head does not define the helix, but is merely placedtherewithin. It is also noted that if a shaft of a tool, such as shaft340 of depth-finding tool 330, described hereinbelow with reference toFIGS. 3A, 3B, and 3D, is inserted into helical tissue-coupling element30, the area into which the shaft of the tool is extends is still“shaftless” because the shaft does not define the helix, but is merelyplaced therewithin.

For some applications, helical tissue-coupling element 30, as well asthe other helical tissue-coupling elements described herein, ismanufactured by laser cutting a tube. The tube typically has a constantwall thickness, which provides the constant radial thickness T_(R). Forsome applications, helical tissue-coupling element 30 (as well as theother helical tissue-coupling elements described herein) comprises oneor more standard implantable alloys known in the art of biomedicalimplants, such as those described in ISO 5832 parts 1-14. For someapplications, helical tissue-coupling element 30 (as well as the otherhelical tissue-coupling elements described herein) comprises a surfacefinish or coating, for promoting tissue integration. The surface finishor coating may be applied to one or more surfaces of the element, suchas the surface that faces radially inward.

Providing the constant radial thickness T_(R) along a substantialportion of helical tissue-coupling element 30 provides a constant innerdiameter along the portion. In contrast, if the radial thickness variedsubstantially (e.g., more than 10%), the tissue-coupling element mighttear the soft tissue.

Typically, for cardiac applications, axial length L is at least 3 mm,such as at least 4 mm, e.g., at least 4.5 mm, and/or less than 20 mm,such as less than 10 mm, such as to prevent damaging coronary vessels.Shaftless helical portion 50 is shaped so as to define and radiallysurround an empty space 52, which typically extends along at least 50%,such as 100%, of axial length L. For some applications, empty space 52has an average diameter of at least 1 mm, no more than 10 mm, and/orbetween 1 and 10 mm, measured perpendicular to axis 32. This innerdiameter corresponds to the inner diameter of helical tissue-couplingelement 30.

Typically, for cardiac applications, helical tissue-coupling element 30has an outer diameter D of between 2 and 8 mm. Typically, outer diameterD varies by less than 10% along entire length L, such as is constantalong entire length L. Typically, helical tissue-coupling element 30 hasan average axial thickness T_(A), measured along entire length L, ofbetween 0.2 and 2 mm. Typically, helical tissue-coupling element 30 hasan average radial thickness T_(R), measured along entire length L, ofbetween 0.2 and 2 mm. Typically, radial thickness T_(R) varies by lessthan 25% along entire length L, such as is constant along entire lengthL.

Helical tissue-coupling element 30 behaves as a spring. For someapplications, a spring constant of helical tissue-coupling element 30,measured along the entire axial length L thereof, during application ofan axial force that does not cause plastic deformation, is between 5 and50 N/mm.

For some applications, helical tissue-coupling element 30 has:

-   -   at least a first axial thickness T_(A1) along a first axial        portion 60 of shaftless helical portion 50 of helical        tissue-coupling element 30, which axial thickness is typically        between 0.2 and 1 mm, and    -   at least a second axial thickness T_(A2) along a second axial        portion 62 of shaftless helical portion 50 more distal than        first axial portion 60, which second axial thickness T_(A2) is        greater than first axial thickness T_(A1), the first and second        axial thicknesses being measured along axis 32. Typically,        second axial thickness T_(A2) is between 0.2 and 1 mm.

For some applications, first axial portion 60 extends to head 40. Inthese applications, first axial portion 60 typically does not enter thesoft tissue during implantation of the tissue anchor.

One result of these differing thicknesses is that if excessive tensionis applied to head 40 at proximal end 42 of anchor 20, such as byflexible longitudinal member 118 as described below, helicaltissue-coupling element 30 generally elongates along first axial portion60 before along second axial portion 62. First axial portion 60 thusserves as a mechanical fuse. As described hereinbelow with reference toFIG. 7C, providing first axial portion 60 effectively reduces the forceon the main part of the anchor (e.g., second axial portion 62) whichholds the anchor in place, thereby reducing or eliminating the danger ofunscrewing the anchor, breaking the anchor, or tearing the tissue, bothduring the implantation procedure and thereafter during long-termimplantation of the anchor. Alternatively or additionally, the physicianmay reduce or cease increasing the tension before second axial portion62 elongates, thereby reducing the risk of the elongation causing damageto the tissue in which second axial portion 62 is implanted, and therisk that the tension will pull the anchor from the tissue. For someapplications, the physician monitors and senses the length of firstaxial portion 60 in real time while applying the tension, in order tosense elongation of first axial portion 60. For example, the physicianmay sense the elongation using imaging (e.g., fluoroscopy, computedtomography, echocardiography, sonography (i.e., ultrasound), or MRI)and/or tactile feedback. Typically, first axial portion 60 undergoesplastic deformation when elongated. As a result, excess force applied tothe anchor is absorbed by first axial portion 60, instead of detachingthe anchor from the tissue, or causing failure elsewhere on the anchor.

For some applications, helical tissue-coupling element 30 has a thirdaxial thickness T_(A3), and optionally additional axial thicknesses,such as T_(A4) and T_(A5), along a third axial portion 64 of shaftlesshelical portion 50 of helical tissue-coupling element 30 more distalthan second axial portion T_(A2), which third axial thickness T_(A3) isless than second axial thickness T_(A2). Typically, third axialthickness T_(A3) is between 0.2 and 2 mm. For some applications, theaxial thickness of third axial portion 64 tapers toward distal end 36,such that T_(A5) is less than T_(A4), which is less than T_(A3). Thistapering may provide easier entry of helical tissue-coupling element 30into the soft tissue. (Third axial thickness T_(A3) may or may not beequal to first axial thickness T_(A1).)

For some applications, the axial thickness of helical tissue-couplingelement 30 varies generally continuously along at least an axial portionof the helical tissue-coupling element, such that helicaltissue-coupling element 30 has (a) first axial thickness T_(A1) at onlya single axial location along first axial portion 60, (b) second axialthickness T_(A2) at only a single axial location along second axialportion 62, and/or (c) third axial thickness T_(A3) at only a singleaxial location along third axial portion 64.

Alternatively or additionally, the axial thickness of helicaltissue-coupling element 30 is constant along one or more axial portionsof the helical tissue-coupling element, such that helicaltissue-coupling element 30 has (a) first axial thickness T_(A1) at aplurality of axial locations along first axial portion 60, (b) secondaxial thickness T_(A2) at a plurality of axial locations along secondaxial portion 62, and/or (c) third axial thickness T_(A3) at a pluralityof axial locations along third axial portion 64.

For some applications, helical tissue-coupling element 30 has:

-   -   a first axial stiffness along first axial portion 60 of        shaftless helical portion 50 of helical tissue-coupling element        30,    -   a second axial stiffness along second axial portion 62 of        shaftless helical portion 50 of helical tissue-coupling element        30 (more distal than first axial portion 60), which second axial        stiffness is greater than the first axial stiffness, and    -   optionally, a third axial stiffness along third axial portion 64        of shaftless helical portion 50 of helical tissue-coupling        element 30 (more distal than second axial portion 62), which        third axial stiffness is less than the second axial stiffness        (the third axial stiffness may or may not be equal to the first        axial stiffness).

As used in the present application, including in the claims, “axialstiffness” means the extent to which the helical tissue-coupling elementresists axial elastic elongation in response to an applied axial force.

For some applications, the second axial stiffness is at least 120% ofthe first axial stiffness. For some applications, the first axialstiffness is between 1 and 100 N/mm, and/or the second axial stiffnessis between 1.2 and 200 N/mm. For some applications, the second axialstiffness is at least 120% of the third axial stiffness. For someapplications, the third axial stiffness is between 1 and 100 N/mm.

These varying axial stiffnesses may be achieved by varying thethicknesses of the axial portions, as described above. Alternatively,these varying axial stiffnesses may be achieved by varying thickness,geometric shape, and/or material properties. For example, materialproperties may be varied by local heat treatment.

For some applications, helical tissue-coupling element 30 has:

-   -   a first axial yield strength along first axial portion 60 of        shaftless helical portion 50 of helical tissue-coupling element        30,    -   a second axial yield strength along second axial portion 62 of        shaftless helical portion 50 of helical tissue-coupling element        30 (more distal than first axial portion 60), which second axial        yield strength is greater than the first axial yield strength,        and    -   optionally, a third axial yield strength along third axial        portion 64 of shaftless helical portion 50 of helical        tissue-coupling element 30 (more distal than second axial        portion 62), which third axial yield strength is less than the        second axial yield strength (the third axial yield strength may        be equal to or different from the first axial yield strength).

As used in the present application, including in the claims, “axialyield strength” means the stress at which the helical tissue-couplingelement begins to axially elongate plastically, rather than onlyelastically.

For some applications, the second axial yield strength is at least 120%of the first axial yield strength. For some applications, the firstaxial yield strength is between 1 and 100 N/mm2, and/or the second axialyield strength is between 1.2 and 200 N/mm2. For some applications, thesecond axial yield strength is at least 120% of the third axial yieldstrength. For some applications, the third axial stiffness is between0.5 and 100 N/mm2.

One result of these differing axial stiffnesses and/or yield strengthsis that if excessive tension is applied to head 40 at proximal end 42 ofanchor 20, helical tissue-coupling element 30 generally elongates alongfirst axial portion 60 before along second axial portion 62, such thatfirst axial portion 60 serves as a mechanical fuse. As describedhereinbelow with reference to FIG. 7C, providing first axial portion 60effectively reduces the force on the main part of the anchor (e.g.,second axial portion 62) which holds the anchor in place, therebyreducing or eliminating the danger of unscrewing the anchor, breakingthe anchor, or tearing the tissue, both during the implantationprocedure and thereafter during long-term implantation of the anchor.Alternatively or additionally, the physician may reduce or ceaseincreasing the tension before second axial portion 62 elongates, therebyreducing the risk of the elongation causing damage to the tissue inwhich second axial portion 62 is implanted, and the risk that thetension will pull the anchor from the tissue. For some applications, thephysician monitors, such as using imaging (e.g., fluoroscopy, computedtomography, echocardiography, sonography, or MRI) or tactile feedback,the length of first axial portion 60 in real time while applying thetension, in order to sense elongation of first axial portion 60.Typically, first axial portion 60 undergoes plastic deformation whenelongated. As a result, excess force applied to the anchor is absorbedby first axial portion 60, instead of detaching the anchor from thetissue, or causing failure elsewhere on the anchor.

For some applications, the axial stiffness of helical tissue-couplingelement 30 varies generally continuously along at least an axial portionof the helical tissue-coupling element, such that helicaltissue-coupling element 30 has (a) the first axial stiffness at only asingle axial location along first axial portion 60, (b) the second axialstiffness at only a single axial location along second axial portion 62,and/or (c) the third axial stiffness at only a single axial locationalong third axial portion 64.

Alternatively or additionally, the axial stiffness of helicaltissue-coupling element 30 is constant along one or more axial portionsof the helical tissue-coupling element, such that helicaltissue-coupling element 30 has (a) the first axial stiffness at aplurality of axial locations along first axial portion 60, (b) thesecond axial stiffness at a plurality of axial locations along secondaxial portion 62, and/or (c) the third axial stiffness at a plurality ofaxial locations along third axial portion 64.

For some applications, the axial yield strength of helicaltissue-coupling element 30 varies generally continuously along at leastan axial portion of the helical tissue-coupling element, such thathelical tissue-coupling element 30 has (a) the first axial yieldstrength at only a single axial location along first axial portion 60,(b) the second axial yield strength at only a single axial locationalong second axial portion 62, and/or (c) the third axial yield strengthat only a single axial location along third axial portion 64.

Alternatively or additionally, the axial yield strength of helicaltissue-coupling element 30 is constant along one or more axial portionsof the helical tissue-coupling element, such that helicaltissue-coupling element 30 has (a) the first axial yield strength at aplurality of axial locations along first axial portion 60, (b) thesecond axial yield strength at a plurality of axial locations alongsecond axial portion 62, and/or (c) the third axial yield strength at aplurality of axial locations along third axial portion 64.

For some applications, an axial length of first axial portion 60 isbetween 10% and 50% of axial length L of helical tissue-coupling element30. Alternatively or additionally, for some applications, an axiallength of second axial portion 62 is between 10% and 50% of axial lengthL of helical tissue-coupling element 30. Alternatively or additionally,for some applications, an axial length of third axial portion 64 isbetween 10% and 30% of axial length L of helical tissue-coupling element30.

Reference is still made to FIGS. 1A-B. For some applications, helicaltissue-coupling element 30 is shaped so as to define:

-   -   a first surface 100 along a first axial surface characteristic        portion 102 of shaftless helical portion 50 of the helical        tissue-coupling element, which first surface 100 has a first        surface characteristic (for example, the first surface        characteristic may be a high level of smoothness), and    -   a second surface 104 along a second axial surface characteristic        portion 106 of shaftless helical portion 50 of the helical        tissue-coupling element different from first axial surface        characteristic portion 102, which second surface 104 has a        second surface characteristic that is configured to mechanically        inhibit rotation of the helical tissue-coupling element to a        greater extent than does the first surface characteristic,        immediately upon advancing of the helical tissue-coupling        element into tissue (e.g., even before any differential tissue        growth that may occur along second surface 104).

First and second surfaces 100 and 104 face in a same spatial direction,such as proximally (as shown), radially outward (not shown), radiallyinward (not shown), or distally (not shown).

For some applications, second axial surface characteristic portion 106is more proximal than first axial surface characteristic portion 102(shown, but not labeled in FIG. 1A; third axial surface characteristicportion 110, described below, may also be considered to be the firstaxial surface characteristic portion).

Alternatively, second axial surface characteristic portion 106 portionis more distal than first axial surface characteristic portion 102 (aslabeled in FIG. 1A). Optionally, first axial surface characteristicportion 102 extends to head 40. Typically, first axial surfacecharacteristic portion 102 does not enter the soft tissue duringimplantation of the tissue anchor.

For some applications, helical tissue-coupling element 30 is shaped soas to define a third surface 108 along a third axial surfacecharacteristic portion 110 of shaftless helical portion 50 of thehelical tissue-coupling element more distal than second axial surfacecharacteristic portion 106, which third surface 108 includes a thirdsurface characteristic that is configured to inhibit the rotation of thehelical tissue-coupling element to a lesser extent than does the secondsurface characteristic (for example, the third surface characteristicmay be a high level of smoothness, which may aid with easy insertion ofthe anchor into soft tissue). First, second, and third surfaces 100,104, and 108 face in a same spatial direction, such as proximally (asshown), radially outward (not shown), radially inward (not shown), ordistally (not shown). For some applications, the first and third surfacecharacteristics are configured to inhibit the rotation of the helicaltissue-coupling element to a same extent.

For some applications, helical tissue-coupling element 30 is configuredto rotate in a first rotational direction when being advanced intotissue (e.g., clockwise, as shown), and the second surfacecharacteristic is configured to inhibit rotation of helicaltissue-coupling element 30 in the first rotational direction to a lesserextent than in a second rotational direction (e.g., counterclockwise)opposite the first rotational direction. Second surface 104 thus isconfigured to generally not inhibit the distal advancing (e.g.,screwing) of the helical tissue-coupling element into the tissue, andinhibit the proximal removal (e.g., unscrewing) of the helicaltissue-coupling element from the tissue, in order to provide betteranchoring of the helical tissue-coupling element in the tissue.

For some applications, second surface 104 is sawtooth-shaped so as toprovide the second surface characteristic. Typically, sawtooth-shapedsecond surface 104 does not define any cutting surfaces. For someapplications, teeth of the sawtooth-shaped second surface have a sharpleading angle β (beta) of between 5 and 25 degrees, and a blunt trailingedge angle γ (gamma) □ of between 75 and 120 degrees.

Alternatively or additionally, for some applications, the second surfacecharacteristic is increased surface roughness.

For some applications, an axial length of first axial surfacecharacteristic portion 102 is between 10 and 800 microns, such asbetween 150 and 800 microns, e.g., between 350 and 600 microns.Alternatively or additionally, for some applications, an axial length ofsecond axial surface characteristic portion 106 is between 10 and 800microns, such as between 150 and 800 microns, e.g., between 350 and 600microns. Alternatively or additionally, for some applications, an axiallength of third axial surface characteristic portion 110 is between 10and 800 microns, such as between 150 and 800 microns, e.g., between 150and 400 microns. Alternatively or additionally, for some application,the axial length of first axial surface characteristic portion 102 is atleast 10%, such as at least 25% of the axial length of second axialsurface characteristic portion 106, and/or no more than 30% of the axiallength of second axial surface characteristic portion 106, for examplebetween 10% and 30% of the axial length of second axial surfacecharacteristic portion 106.

Alternatively or additionally, for some applications, the axial lengthof first axial surface characteristic portion 102 is between 10% and 30%of axial length L of helical tissue-coupling element 30. Alternativelyor additionally, for some applications, an axial length of second axialsurface characteristic portion 106 is between 20% and 80% of axiallength L of helical tissue-coupling element 30. Alternatively oradditionally, for some applications, an axial length of third axialsurface characteristic portion 110 is between 10% and 70% of axiallength L of helical tissue-coupling element 30.

For some applications, these varying surface characteristics areimplemented in combination with the varying axial thicknesses,stiffnesses, and/or yield strengths described hereinabove. For someapplications:

-   -   first axial surface characteristic portion 102 at least        partially axially overlaps, e.g., axially coincides with, first        axial portion 60; the smoothness of first axial surface        characteristic portion 102 increases the likelihood that first        axial portion 60 plastically deforms, rather than breaks or        cracks, when force is applied thereto; and    -   second axial surface characteristic portion 106 at least        partially axially overlaps, e.g., axially coincides with, second        axial portion 62 and/or third axial portion 64, such that the        portions of the helical tissue-coupling element having the        greatest rotation-inhibition properties and axial thickness,        axial stiffness, and/or axial yield strength are the primary        load-bearing surfaces.

Alternatively, these varying surface characteristics are implementedwithout the varying axial thicknesses, stiffnesses, and/or yieldstrengths described hereinabove.

For some applications, helical tissue-coupling element 30 has one ormore of the following characteristics:

-   -   along at least shaftless helical portion 50, such as along        entire length L, a ratio between (a) an average axial thickness        T_(AF) of free space between adjacent turns of the helix and (b)        an average axial thickness T_(A) of the helix is at least 1.5,        no more than 6, and/or between 1.5 and 6. The inter-turn free        space is occupied by soft tissue once the anchor has been        implanted. This ratio may depend in part on the material of the        helix. For example, a ratio at or near the lower end of this        range may be most appropriate for applications in which the        helix comprises stainless steel (e.g., 316LVM), while a ratio at        or near the higher end of this range may be most appropriate for        applications in which the helix comprises a CoCr alloy    -   along at least shaftless helical portion 50, such as along        entire length L, an average axial thickness T_(A) of between 0.2        and 2 mm;    -   along at least shaftless helical portion 50, such as along        entire length L, an average radial thickness T_(R) of between        0.2 and 2 mm;    -   along at least shaftless helical portion 50, such as along        entire length L, a helix angle α (alpha) of less than 25        degrees, such as less than 15 degrees; and/or    -   along at least shaftless helical portion 50, such as along        entire length L, a ratio of outer diameter D to radial thickness        T_(R) is at least 3, no more than 10, and/or between 3 and 10,        such as 5.

The parameters provided for these characteristics provide an acceptablebalance in order to meet three competing requirements. If too steep ahelix angle is provided, the resulting friction is too low and theanchor may unscrew. On the other hand, if too shallow a helix angle isprovided, there may not be enough space between the helical flights forthick enough tissue in order to prevent tissue tear, or a thick enoughmetal of the helix to prevent plastic deformation.

Reference is still made to FIGS. 1A-B. For some applications, head 40comprises a shaft 114, which is coupled (e.g., welded) to a proximal endof helical tissue-coupling element 30, typically such that the shaft andthe helical tissue-coupling element are rotationally fixed to eachother. (The helical tissue-coupling element may have a reduced pitch, oran axially-solid portion, to enable better coupling to the head.) Forsome applications, head 40 comprises an interface 116, which is coupledto a flexible longitudinal member 118, such as described hereinbelowwith reference to FIGS. 7A-D. Optionally, interface 116 is configured torotate with respect to helical tissue-coupling element 30 and shaft 114,in order to provide freedom of movement to flexible longitudinal member118 after implantation of the tissue anchor.

Reference is now made to FIGS. 2A-B, which are schematic illustrationsof a tissue anchor 120, in accordance with an application of the presentinvention. FIG. 2A is an isometric view of the anchor, and FIG. 2B is across-sectional view taken along line IIB-IIB of FIG. 2A. Tissue anchor120 comprises a helical tissue-coupling element 130 disposed about alongitudinal axis 132 thereof and having a distal tissue-penetrating tip134 at a distal end 136 of tissue anchor 120. Typically, tissue anchor120 is shaped so as to define a head 140 at a proximal end 142 thereof.Tissue anchor 120 may be implemented in combination with the features oftissue anchor 20, described hereinabove with reference to FIGS. 1A-B.

Helical tissue-coupling element 130 includes:

-   -   a shaftless single-helix axial portion 150, which is shaped so        as to define a single helical element 152, and    -   a shaftless double-helix axial portion 160 joined to        single-helix axial portion 150 at a junction 161 along helical        tissue-coupling element 130; shaftless double-helix axial        portion 160 is shaped so as to define two helical elements 162        axially offset from each other.        Shaftless single- and double-helix portions 150 and 160 are thus        arranged such that shaftless single-helix portion 150 axially        splits into shaftless double-helix portion 160 at junction 161.        For some applications, shaftless single-helix axial portion 150        extends to distal tip 134. Alternatively or additionally, for        some applications, shaftless double-helix axial portion 160        extends to head 140.

Typically, shaftless double-helix axial portion 160 is proximal toshaftless single-helix axial portion 150. Typically, at least a portionof (typically, the entire) shaftless double-helix axial portion 160 isnot advanced into the soft tissue, but instead remains outside thetissue.

Typically, even though the total combined axial thickness of bothhelices is similar to that of the single helix, the moment of inertia issmaller, resulting in an axial yield strength and/or stiffness ofshaftless single-helix axial portion 150 that is greater than (e.g., atleast 120% greater than) an axial yield strength of shaftlessdouble-helix axial portion 160. For some applications, the axial yieldstrength of shaftless single-helix axial portion 150 is between 1 and100 N, and/or the axial yield strength of shaftless double-helix axialportion 160 is between 1.2 and 200 N.

One result of these differing axial yield strengths and/or stiffnessesis that if excessive tension is applied to head 140 at proximal end 142of anchor 120, helical tissue-coupling element 130 generally elongatesalong shaftless double-helix axial portion 160 before along shaftlesssingle-helix axial portion 150. Shaftless double-helix axial portion 160thus serves as a mechanical fuse. As described hereinbelow withreference to FIG. 7C, providing shaftless double-helix axial portion 160effectively reduces the force applied on the main part of the anchor(e.g., shaftless single-helix axial portion 150) which holds the anchorin place, thereby reducing or eliminating the danger of unscrewing theanchor, breaking the anchor, or tearing the tissue, both during theimplantation procedure and thereafter during long-term implantation ofthe anchor. Alternatively or additionally, the physician may reduce orcease increasing the tension before shaftless single-helix axial portion150 elongates, thereby reducing the risk of the elongation causingdamage to the tissue in which shaftless single-helix axial portion 150is implanted, and the risk that the tension will pull the anchor fromthe tissue. For some applications, the physician monitors, such as usingimaging (e.g., fluoroscopy, computed tomography, echocardiography,sonography, or MRI), the length of shaftless double-helix axial portion160 in real time while applying the tension, in order to senseelongation of shaftless double-helix axial portion 160. Alternatively oradditionally, the physician may sense the elongation using tactilefeedback. Typically, shaftless double-helix axial portion 160 undergoesplastic deformation when elongated. As a result, excess force applied tothe anchor is absorbed by shaftless double-helix axial portion 160,instead of detaching the anchor from the tissue, or causing failureelsewhere on the anchor.

For some applications, two helical elements 162 of shaftlessdouble-helix portion 160 are axially offset from each other, separatedby an axial gap 164. For some applications:

-   -   shaftless single-helix axial portion 150 has a single-helix        axial thickness T_(AS) at a first location on shaftless        single-helix axial portion 150 at a distance of 250 microns from        junction 161, the distance measured circumferentially around        helical tissue-coupling element 130,    -   shaftless double-helix axial portion 160, including two helical        elements 162 and axial gap 164, has a double-helix axial        thickness T_(AD) at a second location on the shaftless        double-helix axial portion at the distance from junction 161,        the single-helix and double-helix axial thicknesses being        measured along axis 132, and    -   double-helix axial thickness T_(AD) equals between 75% and 120%,        e.g., between 95% and 105%, of single-helix axial thickness        T_(AS), such as 100%.

For some applications, shaftless double-helix portion 160 is shaped soas to define two helical elements 162 rotationally offset from eachother by between 160 and 200 degrees, such as 180 degrees, which maycancel out or reduce any moments of force.

For some applications in which tissue anchor 120 is shaped so as todefine head 140 at proximal end 142, shaftless double-helix axialportion 160 extends to the head. For some applications, helicaltissue-coupling element 130 has an axial length of at least 3 mm, andshaftless single- and double-helix portions 150 and 160 collectivelyextend along at least 75% of the axial length of helical tissue-couplingelement 130.

For some applications, tissue anchor 120 is implemented in combinationwith the features of tissue anchors 20 and/or 220, described herein withreference to FIGS. 1A-B and 8A-C, respectively, and may have thedimensions of these tissue anchors.

Reference is now made to FIGS. 3A-F, which are schematic illustrationsof a tissue anchor 320 and a depth-finding tool 330, in accordance withan application of the present invention. FIGS. 3A and 3C-F are isometricviews of the anchor and the depth-finding tool, and FIG. 3B is across-sectional view taken along line IIIB-IIIB of FIG. 3A. Tissueanchor 320 may be implemented in combination with the features of tissueanchors 20, 120, and/or 220, described herein with reference to FIGS.1A-B, 2A-B, and 8A-C, respectively. In this configuration, helicaltissue-coupling element 30 is shaped so as to define and radiallysurround empty space 52 that extends along at least 75% of axial lengthL. In other words, helical tissue-coupling element 30 is not shaped soas to define a shank or shaft, i.e., is shaftless, as definedhereinabove.

Tissue anchor 320 is shaped so as to define a longitudinal channel 350extending from proximal end 42 to distal end 36. Typically, longitudinalaxis 32 runs through the channel, and may be coaxial therewith.Typically, a distal portion of channel 350 coincides with empty space52, and a proximal portion of the channel is defined by head 40. Forsome applications, the distal portion of the channel is wider than theproximal portion of the channel, as shown in FIGS. 3A-B.

Depth-finding tool 330 comprises (a) a radiopaque bead 342 shaped so asto define a hole 344 therethrough, and, typically, (b) a shaft 340.Typically, a distal tip of shaft 340 is sharp.

Shaft 340 of depth-finding tool 330 is removably positioned withinchannel 350, typically coaxially with longitudinal axis 32, such thatthe shaft passes through the hole of the bead, and the bead is slidablealong the shaft. Bead 342 is positioned within the distal portion of thechannel, in empty space 52. The bead is typically initially positionedat or near distal end 36 of tissue anchor 320, as shown in FIGS. 3A-B.For some applications, helical tissue-coupling element 30 is shaped soas to define a distal stopper 360 that prevents bead 342 from advancingdistally off of shaft 340.

Bead 342 serves as a marker that indicates a depth of penetration ofhelical tissue-coupling element 30 into soft tissue, such as cardiactissue. When rotated, helical tissue-coupling element 30 penetrates andis advanced into the tissue. Bead 342 does not penetrate the tissue, andthus remains at the surface of the tissue, in contact therewith. As aresult, as the tissue-coupling element advances into the tissue, thebead remains stationary, and moves toward proximal end 42 of anchor 320(and toward head 40). In other words, proximal end 42 of anchor 320 (andhead 40) move closer to bead 342, as measured along axis 32.

Typically, as anchor 320 is screwed into the tissue, shaft 340 ofdepth-finding tool 330 penetrates and advances into the tissue alongwith the anchor. For some applications, when the shaft penetrates to acertain depth, the shaft is withdrawn slightly. Typically, after anchor320 has been fully implanted, shaft 340 is withdrawn entirely from thetissue, and removed from the patient's body. Optionally, the sharpdistal tip of shaft 340 is inserted into the tissue slightly, evenbefore insertion of anchor 320, in order to prevent sliding ofdepth-finding tool 330 and the anchor on the surface of the tissuebefore commencement of insertion of the anchor into the tissue.

For some applications, depth-finding tool 330 is implemented incombination with techniques described with reference to FIGS. 22A-B ofU.S. patent application Ser. No. 13/553,081, filed Jul. 19, 2012, whichpublished as US Patent Application Publication 2013/0018459 and isassigned to the assignee of the present application and is incorporatedherein by reference. For these applications, in addition to its functiondescribed herein, shaft 340 serves as elongate longitudinal element 2610described in the '081 application, for reversibly coupling the head ofthe anchor to the delivery tool. Proximal withdrawal of the shaftunlocks the positive connection of the head of the anchor with thedelivery tool.

Both the bead and more proximal portions of the anchor (such as head 40)are viewed using imaging (e.g., fluoroscopy, computed tomography,echocardiography, sonography, or MRI), and the distance between the beadand the proximal end of the anchor (e.g., the head) is estimated andmonitored in real time as the anchor is advanced into the tissue. Whenthe bead reaches a desired distance from the head (such as reaches thehead itself), the tissue-coupling element has been fully advanced, e.g.,screwed, into and embedded in the tissue, and the physician thus ceasesrotating the anchor. The physician proximally withdraws shaft 340 fromchannel 350, leaving the bead at the proximal end of empty space 52;helical tissue-coupling element 30 contains the bead.

Without using a technique such as this for visualizing the advancementof the anchor into the tissue, it is often difficult to ascertain whenthe tissue anchor has been fully embedded into the tissue, because thetissue is difficult to see in some images, such as fluoroscopic images.As a result, the tissue anchor may inadvertently be insufficientlyadvanced into the tissue, resulting in poor anchoring in the tissue, orover-advanced into the tissue, possible tearing or otherwise damagingthe tissue.

Bead 342 may have any appropriate shape, such as a sphere (as shown) ora disc (not shown). An outer diameter of the bead is typically slightlygreater than the inner diameter of empty space 52, in order to providesome friction between the bead and the helical tissue-coupling element30, and prevent the bead from being free-floating within the helix. Forexample, the outer diameter of the bead may be between 0.05 microns lessthan and 100 microns greater than the inner diameter of empty space 52.Alternatively or additionally, the bead comprises a coating whichprovides some friction between the bead and the helix; the coating maybe sheared off as the bead moves proximally through the helix. Furtheralternatively or additionally, the bead and shaft are configured toprovide some friction therebetween. For some applications, the outerdiameter of the bead may be between 1 and 5 mm.

For some applications, as shown in FIGS. 3C and 3D, depth-finding tool330 further comprises a wire 362 which is at least partially (e.g.,entirely) disposed within channel 350 and couples bead 342 to a proximalportion of the anchor, such as head 40, thereby preventing the bead fromexiting the distal end of the channel. Wire 362 is very thin, so as tonot resist proximal motion of the bead. Wire 362 is optionally shaped asa helical spring having a very low spring constant (as shown). FIG. 3Cshows a configuration without shaft 340, while FIG. 3D shows aconfiguration that includes shaft 340.

Further alternatively or additionally, shaft 340 may be configured toprevent distal motion of the bead. For example, the shaft may bethreaded (such as in the opposite direction to the thread of helicaltissue-coupling element 30), or be shaped so as to define an angularlocking mechanism that locks with the bead at certain rotationalorientations, and unlocks with the bead at other rotationalorientations.

FIGS. 3E-F show a configuration without shaft 340, and include exemplaryx-ray images (still radiographs taken using fluoroscopy) taken in anexperiment conducted by the inventors in accordance with an applicationof the present invention. The inventors performed an ex vivo study as aproof-of-concept of some of the imaging-based the depth-findingtechniques described herein. In particular, the inventors constructed amock-up of tissue anchor 320 and depth-finding tool 330. The inventorsfabricated a tissue anchor similar to tissue anchor 320, and adepth-finding tool similar to depth-finding tool 330 (the configurationwithout shaft 340). The inventors used animal meat (ribs) to simulatecardiac soft tissue, and placed the meat under an aluminum block tosimulate thoracic fluoroscopy.

FIG. 3E includes an x-ray image of the tissue anchor advanced partiallyinto the tissue, with the radiopaque bead resting against the surface ofthe tissue. FIG. 3F includes an x-ray image of the tissue anchor andbead after the tissue anchor is fully rotated into the tissue. As can beclearly seen in these x-ray images, the bead remained at the surface ofthe tissue, and thus moved proximally toward the head of the anchor asthe anchor was screwed into the tissue. This ex vivo experiment thusdemonstrated that the position of radiopaque bead with respect to theanchor head could be easily seen using conventional x-ray imaging.

Reference is now made to FIGS. 4A-B, which are schematic illustrationsof a tissue anchor 420, in accordance with an application of the presentinvention. FIG. 4A is an isometric view of the anchor, and FIG. 4B is across-sectional view taken along line IVB-IVB of FIG. 4A. Tissue anchor420 may be implemented in combination with the features of tissueanchors 20, 120, and/or 220, described herein with reference to FIGS.1A-B, 2A-B, and 8A-C, respectively. For some applications, axialthickness T_(A) is constant, or varies by less than 5%, such as by lessthan 3%, along all or a portion of the axial length of tissue anchor420.

Like tissue anchors 20, 120, and 220, tissue anchor 420 compriseshelical tissue-coupling element 30, which is disposed about longitudinalaxis 32 thereof and has distal tissue-penetrating tip 34. Typically,tissue anchor 420 has axial length L of at least 3 mm, no more than 20mm (e.g., no more than 10 mm), and/or between 3 mm and 20 mm, such asbetween 3 mm and 10 mm. Typically, helical tissue-coupling element 30 isshaped so as to define and radially surround empty space 52 that extendsalong at least 75% of axial length L. In other words, the helicaltissue-coupling element typically is not shaped so as to define a shankor shaft.

Tissue anchor 420 further comprises a radiopaque bead 430 shaped so asto define a hole 432 therethrough. Helical tissue-coupling element 30passes through hole 432 of bead 430, such that the bead is slidablealong the helical tissue-coupling element. Bead 430 thus serves as amarker that indicates a depth of penetration of the tissue-couplingelement into soft tissue 530, such as cardiac tissue. (Becausetissue-coupling element 30 is helical, bead 430 moves along element 30in a helical path.)

When rotated, helical tissue-coupling element 30 penetrates and isadvanced into tissue 530. Bead 430 does not penetrate the tissue, andthus remains at a surface 552 of tissue 530, in contact therewith. As aresult, as the tissue-coupling element advances into the tissue, thebead remains stationary and slides along the tissue-coupling elementtoward proximal end 42 of anchor 420 (and toward head 40). In otherwords, proximal end 42 of anchor 420 (and head 40) move closer to bead430, as measured along axis 32. Both the bead and more proximal portionsof the anchor (such as head 40) are viewed using imaging (e.g.,fluoroscopy, computed tomography, echocardiography, sonography, or MRI),and the distance between the bead and the proximal end of the anchor(e.g., the head) is estimated and monitored in real time as the anchoris advanced into the tissue. When the bead reaches a desired distancefrom the head (such as reaches the head itself), the tissue-couplingelement has been fully advanced, e.g., screwed, into and embedded in thetissue, and the physician thus ceases rotating the anchor.

Without using a technique such as this for visualizing the advancementof the anchor into the tissue, it is often difficult to ascertain whenthe tissue anchor has been fully embedded into the tissue, becausetissue 530 is difficult to see in some images, such as fluoroscopicimages. As a result, the tissue anchor may inadvertently beinsufficiently advanced into the tissue, resulting in poor anchoring inthe tissue, or over-advanced into the tissue, possible tearing orotherwise damaging the tissue.

For some applications, helical tissue-coupling element 30 defines secondsurface 104, which is configured to inhibit unscrewing of the helicaltissue-coupling element from the tissue, as described hereinabove withreference to FIGS. 1A-B. For some of these applications, the physicianmonitors the position of the bead with respect to a distal end 440 ofsecond axial surface characteristic portion 106 (which defines secondsurface 104) (either by directly observing the position with respect todistal end 440, or indirectly assessing the position with respect todistal end 440, such as by assessing the position of the bead withrespect to proximal end 42 of anchor 420, e.g., head 40). Duringrotation of helical tissue-coupling element 30 into the tissue, the beadreaches distal end 440 immediately before second axial surfacecharacteristic portion 106 penetrates surface 552 of tissue 530. Beforefurther advancing the helical tissue-coupling element into the tissue,the physician may apply tension, such as described hereinbelow withreference to FIG. 7C, for example in order to assess whether the anchoris placed in an appropriate location for altering the geometry of theright atrium sufficiently to repair the tricuspid valve. If the locationis found not to be appropriate, the physician may remove the anchor fromthe tissue and redeploy the anchor at another location. The anchor maygenerally be readily unscrewed from the tissue because second surface104 did not yet enter the tissue. If the location is found to beappropriate, the physician further advances helical tissue-couplingelement 30 into the tissue, optionally using bead 430 to assess when thetissue-coupling element has been completely screwed into the tissue.

For some applications, helical tissue-coupling element 30 is shaped soas define a distal stopper 450, which protrudes from the tissue-couplingelement sufficiently to prevent motion of bead 430 distally beyond thestopper. Bead 430 is threaded around the tissue-coupling elementproximal to the stopper. The stopper may protrude in one or moredirections from the tissue-coupling element. By way of illustration, thestopper is shown in FIG. 4A as protruding radially outwardly from thetissue-coupling element.

Bead 430 may have any appropriate shape, such as annular, e.g., arectangle, e.g., square (as shown). Typically, the inner shape of thebead generally conforms with, and is slightly larger than, the outercross-sectional shape of the helix.

Reference is now made to FIGS. 5A-C and 6, which are schematicillustrations of a tissue anchor 520 at several stage of implantation insoft tissue 530, in accordance with respective applications of thepresent invention. Tissue anchor 520 may be implemented in combinationwith the features of tissue anchors 20, 120, 220, and/or 420 describedherein with reference to FIGS. 1A-B, 2A-B, 8A-C, and 4A-B, respectively.For some applications, axial thickness T_(A) is constant, or varies byless than 5%, such as by less than 3%, along all or a portion of theaxial length of tissue anchor 520.

Like tissue anchors 20, 120, 220, and 420, tissue anchor 520 compriseshelical tissue-coupling element 30, which is disposed about longitudinalaxis 32 thereof and has distal tissue-penetrating tip 34. Typically,tissue anchor 520 has axial length L of at least 3 mm, no more than 20mm (e.g., no more than 10 mm), and/or between 3 mm and 20 mm, such asbetween 3 mm and 10 mm. Typically, helical tissue-coupling element 30 isshaped so as to define and radially surround empty space 52 that extendsalong at least 75% of axial length L. In other words, the helicaltissue-coupling element typically is not shaped so as to define a shankor shaft.

Tissue anchor 520 further comprises a plurality of radiopaque beads 430,e.g., exactly two radiopaque beads 430A and 430B, shaped so as to definerespective holes therethrough, such as shown in FIGS. 4A-B. Helicaltissue-coupling element 30 passes through the holes of beads 430, suchthat the beads are slidable along the helical tissue-coupling element.Beads 430 thus serve as markers that indicate a depth of penetration ofthe tissue-coupling element into soft tissue, such as cardiac tissue.

For some applications, helical tissue-coupling element 30 defines secondsurface 104, which is configured to inhibit unscrewing of the helicaltissue-coupling element from the tissue, as described hereinabove withreference to FIGS. 1A-B.

As shown in FIG. 5A, for some applications, before helicaltissue-coupling element 30 is inserted into soft tissue 530, such ascardiac tissue, a first radiopaque bead 430A is initially positionednear distal tissue-penetrating tip 34, distal to distal end 440 ofsecond axial surface characteristic portion 106 (which defines secondsurface 104), and a second radiopaque bead 430B is initially positionedproximal to and near a proximal end 550 of second axial surfacecharacteristic portion 106.

As shown in FIG. 5B, the physician begins advancing helicaltissue-coupling element 30 into tissue 530. When rotated, helicaltissue-coupling element 30 penetrates and is advanced into the tissue.First bead 430A does not penetrate the tissue, and thus remains atsurface 552 of the tissue, in contact therewith. As a result, as thetissue-coupling element advances into the tissue, first bead 430Aremains stationary and slides along the tissue-coupling element towardproximal end 42 of anchor 520 (and toward head 40). In other words,proximal end 42 and anchor 520 (and head 40) move closer to first bead430A, as measured along axis 32. In addition, first bead 430A movescloser to second bead 430B, which has advanced distally as the anchor isscrewed into the tissue. Both the beads and more proximal portions ofthe anchor (such as head 40) are viewed using imaging (e.g.,fluoroscopy, computed tomography, echocardiography, sonography, or MRI),and the distance between first bead 430A and the proximal end of theanchor (e.g., the head), and/or between first and second beads 430A and430B, is estimated and monitored in real time as the anchor is advancedinto the tissue.

By assessing one or more of the distances described above, the physicianmonitors the position of first bead 430A with respect to distal end 440of second axial surface characteristic portion 106 (which defines secondsurface 104). During rotation of helical tissue-coupling element 30 intothe tissue, first bead 430A reaches distal end 440 immediately beforesecond axial surface characteristic portion 106 penetrates the surfaceof the tissue. Before further advancing the helical tissue-couplingelement into the tissue, the physician may apply tension, such asdescribed hereinbelow with reference to FIG. 7C, for example in order toassess whether the anchor is placed in an appropriate location foraltering the geometry of the right atrium sufficiently to repair thetricuspid valve. If the location is found not to be appropriate, thephysician may remove the anchor from the tissue and redeploy the anchorat another location. The anchor may generally be readily unscrewed fromthe tissue because second surface 104 did not yet enter the tissue.

If the location is found to be appropriate, the physician furtheradvances helical tissue-coupling element 30 into tissue 530, as shown inFIG. 5C. As mentioned above, second bead 430B is initially positionedproximal to and near proximal end 550 of second axial surfacecharacteristic portion 106 (as shown in FIGS. 5A and 5B). The physicianuses second bead 430B to assess when the tissue-coupling element hasbeen completely screwed into tissue 530. As helical tissue-couplingelement 30 further penetrates and is advanced into the tissue, secondbead 430B does not penetrate the tissue, and thus remains at surface 552of the tissue, in contact therewith, as shown in FIG. 5C. As a result,as the tissue-coupling element advances into the tissue, second bead430B remains stationary and slides along the tissue-coupling elementtoward proximal end 42 of anchor 520 (and toward head 40). Both secondbead 430B and more proximal portions of the anchor (such as head 40) areviewed using imaging (e.g., fluoroscopy, computed tomography,echocardiography, sonography, or MRI), and the distance between secondbead 430B and the proximal end of the anchor (e.g., the head), isestimated and monitored in real time as the anchor is advanced into thetissue. As shown in FIG. 5C, when second bead 430B reaches a desireddistance from the head (such as reaches the head itself), thetissue-coupling element has been fully advanced, e.g., screwed, into andembedded in the tissue, and the physician thus ceases rotating theanchor.

Without using a technique such as this for visualizing the advancementof the anchor into the tissue, it is often difficult to ascertain whenthe tissue anchor has been fully embedded into the tissue, because thetissue is difficult to see in some images, such as fluoroscopic images.As a result, the tissue anchor may inadvertently be insufficientlyadvanced into the tissue, resulting in poor anchoring in the tissue, orover-advanced into the tissue, possible tearing or otherwise damagingthe tissue.

For some applications, as shown in FIG. 5C, tissue anchor 520 isconfigured such that during advancement of the tissue anchor into tissue530, first bead 430A is stopped at distal end 440 of second axialsurface characteristic portion 106 from further proximal sliding bysecond surface 104. First bead 430A thus enters tissue 530 with theanchor as the anchor is further rotated and advanced into the tissue.

Alternatively, for other applications, as shown in FIG. 6, tissue anchor520 is configured such that during advancement of the tissue anchor intotissue 530, first bead 430A remains at surface 552 of tissue 530 andslides over second axial surface characteristic portion 106. For theseapplications, second bead 430B is typically initially fixed at aproximal end of tissue-coupling element 30. As the tissue anchor isfurther advanced into the tissue, first and second beads 430A and 430Bthus become positioned adjacent to each other, marking the desiredpenetration depth. (It may be easier for the physician to assess thedistance between first and second beads 430A and 430B using imaging,than between first bead 430A and proximal end 42 (e.g., the head) of theanchor.)

For some applications, helical tissue-coupling element 30 is shaped soas define distal stopper 450, described hereinabove with reference toFIGS. 4A-B.

First and second beads 430A and 430B may have any appropriate shape,such as annular, e.g., a rectangle, e.g., square (as shown). Typically,the inner shape of the bead generally conforms with, and is slightlylarger than, the outer cross-sectional shape of the helix at itsgreatest thickness.

Reference is now made to FIGS. 7A-D, which are schematic illustrationsof a system 620 comprising a first tissue-engaging element 660 a and asecond tissue-engaging element 660 b for repairing a tricuspid valve 604of a heart 602 of a patient, in accordance with some applications of thepresent invention. First tissue-engaging element 660 a comprises tissueanchor 20, tissue anchor 120, tissue anchor 220, tissue anchor 320,tissue anchor 420, or tissue anchor 520, described herein with referenceto FIGS. 1A-B, 2A-B, 8A-C, 4A-B, 5A-B, and 6A-C and 7, respectively. Byway of illustration and not limitation, in the configuration shown inFIGS. 7A-D, first tissue-engaging element 660 a comprises tissue anchor120, described hereinabove with reference to FIGS. 2A-B. Firsttissue-engaging element 660 a is designated for implantation at least inpart in cardiac tissue at a first implantation site 630. Secondtissue-engaging element 660 b comprises a stent 650 which is designatedfor implantation at a second implantation site 652 in a portion of ablood vessel, e.g., an inferior vena cava 608 (as shown) or a superiorvena cava 610 (although not shown, can be implemented as described withreference to FIGS. 1E-G of PCT Publication WO 2011/089601, which isassigned to the assignee of the present application and is incorporatedherein by reference). First and second tissue-engaging elements 660 aand 660 b are coupled together by flexible longitudinal member 118. Forsome applications, flexible longitudinal member 118 has a length of atleast 10 mm, no more than 40 mm, and/or between 10 and 40 mm. For someapplications, flexible longitudinal member 118 comprises a suture, wire,or cord.

Typically, a distance between first and second implantation sites 630and 652 is adjusted by pulling to apply tension to or relaxinglongitudinal member 118 and/or by applying tension to at least one offirst and second tissue-engaging elements 660 a and 660 b. Responsively,a distance between the leaflets of tricuspid valve 604 is adjusted toreduce and eliminate regurgitation through valve 604, and thereby, valve604 is repaired. For some applications, longitudinal member 118 ispulled or relaxed by manipulating second tissue-engaging element 660 b,as is described hereinbelow.

First and second tissue-engaging elements 660 a and 660 b may befabricated and/or comprise materials as described with reference toFIGS. 1A-G of the above-mentioned '601 publication. For someapplications, second tissue-engaging element 660 b comprises a stent 650which is advanced toward and expandable in a portion of inferior venacava 608 (such as shown in FIGS. 7A-D) or superior vena cava 610 (suchas shown in FIGS. 1E-G of the above-mentioned '601 publication), i.e., ablood vessel that is in direct contact with a right atrium 606 of heart602 of the patient. Second tissue-engaging element 660 b is implanted atsecond implantation site 652. As shown, first implantation site 630comprises a portion of an annulus of tricuspid valve 604. Implantationsite 630 typically comprises a portion of the annulus of valve 604 thatis between (1) the middle of the junction between the annulus andanterior leaflet 614, and (2) the middle of the junction between theannulus and posterior leaflet 616, e.g., between the middle of thejunction between the annulus and anterior leaflet 614 and the commissurebetween the anterior and posterior leaflets. That is, firsttissue-engaging element 660 a is coupled to, e.g., screwed into, thefibrous tissue of the tricuspid annulus close to the commissure inbetween anterior leaflet 614 and posterior leaflet 616. Implantationsite 630 is typically close to the mural side of valve 604. For suchapplications, the drawing together of first and second implantationsites 630 and 652 cinches valve 604 and may create a bicuspidization oftricuspid valve 604, and thereby achieve stronger coaptation betweenanterior leaflet 614 and septal leaflet 612.

For some applications, first implantation site 630 may include a portionof tissue of a wall defining right atrium 606 of heart 602, typically ina vicinity of the annulus of valve 604. For other applications, firstimplantation site 630 may include a portion of a wall of a rightventricle of heart 602, a ventricular portion of the annulus of valve604, or a portion of a papillary muscle of the right ventricle of heart602, as is shown hereinbelow in FIG. 6 of the above-mentioned '601publication. First implantation site 630 is typically a distance awayfrom, e.g., generally opposite, second implantation site 652 so that,following adjusting of longitudinal member 118, first and secondimplantation sites 630 and 652 are drawn together, and thereby at leastfirst and second leaflets, e.g., all three leaflets, of valve 604 aredrawn toward each other. For applications in which first implantationsite 630 includes a portion of tissue of the annulus, the adjusting ofthe distance between implantation sites 630 and 652 alters the geometryof (i.e., changes the configuration of) the annulus of valve 604 andthereby draws together the leaflets of valve 604. For applications inwhich first implantation site 630 includes tissue of a portion of a wallthat defines atrium 606, the adjusting of the distance betweenimplantation sites 630 and 652 alters the geometry of (i.e., changes theconfiguration of) the wall of atrium 606 and thereby draws together theleaflets of valve 604.

FIG. 7A shows the advancement of a catheter 622 toward atrium 606 of thepatient until a distal end 623 of the catheter is disposed within atrium606, as shown. The procedure is typically performed with the aid ofimaging, such as fluoroscopy, transesophageal echo, and/orechocardiography. For some applications, the procedure begins byadvancing a semi-rigid guidewire into right atrium 606 of the patient.The guidewire provides a guide for the subsequent advancement ofcatheter 622 therealong and into the right atrium. Catheter 622typically comprises a 14-20 F sheath, although the size may be selectedas appropriate for a given patient. Catheter 622 is advanced throughvasculature into right atrium 606 using a suitable point of origintypically determined for a given patient, such as described in theabove-mentioned '601 publication.

Once distal end 623 of catheter 622 is disposed within atrium 606, ananchor-deployment tube 624 is extended from within catheter 622 beyonddistal end 623 thereof and toward first implantation site 630.Anchor-deployment tube 624 holds first tissue-engaging element 660 a anda distal portion of longitudinal member 118. For some applications, tube624 is steerable, as is known in the catheter art, while for otherapplications, a separate steerable element may be coupled toanchor-deployment tube 624. Under the aid of imaging guidance,anchor-deployment tube 624 is advanced toward first implantation site630 until a distal end thereof contacts cardiac tissue of heart 602 atfirst implantation site 630. Anchor-deployment tube 624 facilitatesatraumatic advancement of first tissue-engaging element 660 a towardfirst implantation site 630. For such applications in whichanchor-deployment tube 624 is used, stent 650 is compressed within aportion of tube 624.

As shown in FIG. 7B, an anchor-manipulating tool (not shown for clarityof illustration), which is slidably disposed within anchor-deploymenttube 624, is slid distally within tube 624 so as to push distally firsttissue-engaging element 660 a and expose first tissue-engaging element660 a from within tube 624. For some applications of the presentinvention, the anchor-manipulating tool is reversibly coupled to firsttissue-engaging element 660 a and facilitates implantation of firsttissue-engaging element 660 a in the cardiac tissue.

The physician rotates the anchor-manipulating tool from a site outsidethe body of the patient in order to rotate first tissue-engaging element660 a and thereby screw at least a portion of first tissue-engagingelement 660 a in the cardiac tissue. For applications in whichtissue-engaging element 660 a comprises tissue anchor 20, the physiciantypically advances second axial portion 62 (and third axial portion 64,if provided) completely into the cardiac soft tissue, and leaves atleast a portion of (e.g., the entire) first axial portion 60 outside ofthe soft tissue. For applications in which tissue-engaging element 660 acomprises tissue anchor 120, the physician typically advancessingle-helix portion 150 completely into the cardiac soft tissue, andleaves at least a portion of (e.g., the entire) double-helix portion 160outside of the soft tissue. For applications in which tissue-engagingelement 660 a comprises tissue anchor 220, the physician typicallyadvances second axial portion 262 (and third axial portion 264, ifprovided) completely into the cardiac soft tissue, and leaves at least aportion of (e.g., the entire) first axial portion 260 outside of thesoft tissue.

Alternatively, system 620 is provided independently of theanchor-manipulating tool, and anchor-deployment tube 624 facilitatesimplantation of first tissue-engaging element 660 a in the cardiactissue. The physician rotates anchor-deployment tube 624 from a siteoutside the body of the patient in order to rotate first tissue-engagingelement 660 a and thereby screw at least a portion of firsttissue-engaging element 660 a in the cardiac tissue.

For applications in which first tissue-engaging element 660 a comprisestissue anchor 320, tissue anchor 420, or tissue anchor 520, describedhereinabove with reference to FIGS. 3A-F, 4A-B, and 5A-C and 6,respectively, the physician visualizes the respective radiopaque beadsto aid with proper advancement of the anchor into the tissue.

As shown in FIG. 7C, following the implantation of first tissue-engagingelement 660 a at first implantation site 630, anchor-deployment tube 624is retracted within catheter 622 in order to expose longitudinal member118. Subsequently, longitudinal member 118 is tensioned in order torepair tricuspid valve 604, as described hereinbelow.

For some applications, prior to pulling the portion of longitudinalmember 118 that is disposed between first tissue-engaging element 660 aand distal end 623 of catheter 622, a mechanism that facilitates theapplication of a pulling force to longitudinal member 118 is fixed inplace, as described in the above-mentioned '601 publication.

For some applications, catheter 622 is reversibly coupled to a proximalportion of longitudinal member 118 by being directly coupled to theproximal portion of member 118 and/or catheter 622 is reversibly coupledto second tissue-engaging element 60 b. For example, catheter 622 may bereversibly coupled to stent 650 by the stent's application of a radialforce against the inner wall of catheter 622 because of the tendency ofstent 650 to expand radially. Following implantation of firsttissue-engaging element 660 a, catheter 622 (or an element disposedtherein) is then pulled proximally to apply tension to longitudinalmember 118, which, in such an application, functions as a tensioningelement. For some applications, catheter 622 pulls on secondtissue-engaging element 660 b in order to pull longitudinal member 118.For other applications, catheter 622 pulls directly on longitudinalmember 118. For yet other applications, a pulling mechanism pulls onlongitudinal member 118, as is described with reference to FIGS. 7A-D inthe above-referenced '601 publication.

Pulling longitudinal member 118 pulls taut the portion of longitudinalmember 118 that is disposed between first tissue-engaging element 660 aand distal end 623 of catheter 622. Additionally, longitudinal member118 may be pulled or relaxed in order to adjust the distance betweenfirst and second implantation sites 630 and 652. Responsively to thepulling of longitudinal member 118, at least the anterior and septalleaflets of tricuspid valve 604 are drawn together because the geometryof the annulus and/or of the wall of atrium 606 is altered in accordancewith the pulling of longitudinal member 118 and depending on thepositioning of first tissue-engaging element 660 a.

For some applications, during the pulling of longitudinal member 118 bycatheter 622, a level of regurgitation of tricuspid valve 604 ismonitored. Longitudinal member 118 is pulled until the regurgitation isreduced or ceases.

For applications in which first tissue-engaging element 660 a comprisestissue anchor 20, described hereinabove with reference to FIGS. 1A-B, ifthe physician applies too much tension when pulling longitudinal member118, helical tissue-coupling element 30 generally elongates along firstaxial portion 60 before along second axial portion 62, such that firstaxial portion 60 serves as a mechanical fuse. Providing first axialportion 60 effectively reduces the force on the main part of the anchor(e.g., second axial portion 62) which holds the anchor in place, therebyreducing or eliminating the danger of unscrewing the anchor, breakingthe anchor, or tearing the tissue, both during the implantationprocedure and thereafter during long-term implantation of the anchor.Alternatively or additionally, the physician may reduce or ceaseincreasing the tension before second axial portion 62 elongates, therebyreducing the risk of the elongation causing damage to the tissue inwhich second axial portion 62 is implanted, and the risk that thetension will pull the anchor from the tissue. For some applications, thephysician senses elongation of first axial portion 60 in real time whileapplying the tension, such as using imaging (e.g., fluoroscopy, computedtomography, echocardiography, sonography, or MRI) and/or tactilefeedback.

For applications in which first tissue-engaging element 660 a comprisestissue anchor 120, described hereinabove with reference to FIGS. 2A-B,if the physician applies too much tension when pulling longitudinalmember 118, helical tissue-coupling element 130 generally elongatesalong shaftless double-helix axial portion 160 before along single-helixaxial portion 150, and thus can be considered to serve as a mechanicalfuse. Providing shaftless double-helix axial portion 160 effectivelyreduces the force on shaftless single-helix axial portion 150 whichholds the anchor in place, thereby reducing or eliminating the danger ofunscrewing the anchor, breaking the anchor, or tearing the tissue, bothduring the implantation procedure and thereafter during long-termimplantation of the anchor. Alternatively or additionally, the physicianmay reduce or cease increasing the tension before single-helix axialportion 150 elongates, thereby reducing the risk of the elongationcausing damage to the tissue in which single-helix axial portion 150 isimplanted, and the risk that the tension will pull the anchor from thetissue. For some applications, the physician senses elongation ofshaftless double-helix axial portion 160 in real time while applying thetension, such as using imaging (e.g., fluoroscopy, computed tomography,echocardiography, sonography, or MRI) and/or tactile feedback.

For some applications in which first tissue-engaging element 660 acomprises tissue anchor 420 or tissue anchor 520, described hereinabovewith reference to FIGS. 4A-B and FIGS. 5A-C and 6, respectively, thephysician may monitor the location of the bead during implantation ofthe anchor as described with reference to FIG. 7B, and cease advancingthe anchor once the bead reaches distal end 440 immediately beforesecond axial surface characteristic portion 106 penetrates the surfaceof the tissue. Before further advancing the helical tissue-couplingelement into the tissue, the physician may apply tension, in order toassess whether the anchor is placed in an appropriate location foraltering the geometry of the right atrium sufficiently to repair thetricuspid valve. If the location is found not to be appropriate, thephysician may remove the anchor from the tissue and redeploy the anchorat another location. The anchor may generally be readily unscrewed fromthe tissue because second surface 104 did not yet enter the tissue. Ifthe location is found to be appropriate, the physician further advancesthe helical tissue-coupling element into the tissue, optionally usingthe bead to assess when the tissue-coupling element has been completelyscrewed into the tissue.

Once the physician determines that the regurgitation of valve 604 isreduced or ceases, and valve 604 has been repaired, the physiciandecouples catheter 622 from second tissue-engaging element 660 bdisposed therein and/or from longitudinal member 118, and then retractscatheter 622 in order to expose second tissue-engaging element 660 b,i.e., stent 650. During the advancement of catheter 622 toward atrium606, stent 650 is disposed within a distal portion of catheter 622 in acompressed state. Following initial retracting of catheter 622, stent650 is exposed and is allowed to expand and contact a wall of inferiorvena cava 608.

FIG. 7D shows the stent fully exposed and fully expanded. Responsivelyto the expanding, stent 650 is implanted in second implantation site 652and maintains the tension of longitudinal member 118 on firsttissue-engaging element 660 a and thereby on the portion of cardiactissue to which first tissue-engaging element 660 a is coupled.

The techniques described with reference to FIGS. 7A-B may be performedin combination with techniques described in the above-mentioned '601publication, mutatis mutandis.

Reference is now made to FIGS. 8A-C, which are schematic illustrationsof a tissue anchor 220, in accordance with respective applications ofthe present invention. FIG. 8A is an isometric view of the anchor, andFIG. 8B is a cross-sectional view taken along line VIIIB-VIIIB of FIG.8A. FIG. 8C is an isometric view of another configuration of the anchor,which is described hereinbelow. Tissue anchor 220 comprises a helicaltissue-coupling element 230 disposed about a longitudinal axis 232thereof and having a distal tissue-penetrating tip 234 at a distal end236 of tissue anchor 220. Typically, tissue anchor 220 is shaped so asto define a head 240 at a proximal end 242 thereof.

Helical tissue-coupling element 230 comprises a wire 254 shaped as ahelix 256. Wire 254 has a non-circular cross section 264, which istypically shaped as a polygon, such as a quadrilateral, e.g., arectangle 266, for example a square as shown in FIG. 8B, or as anellipse. During manufacture, wire 254 is twisted about its longitudinalaxis, so as to define a ridged surface. The wire, thus twisted, isformed into helix 256, as shown in FIGS. 8A-B. The ridged surface helpsanchor the tissue-coupling element in soft tissue, such as cardiactissue. For some applications, the wire is twisted about itslongitudinal axis at least 1 (e.g., at least 2) twists per cm, no morethan 5 twists per cm, and/or between 1 and 5, e.g., 2 and 5, twists percm of the length of wire 254 (the strut) while the strut is straight(i.e., before curved into the helix).

For applications in which the cross-section is shaped as rectangle 266,each of a length L3 and width W thereof is typically between 0.3 and 0.8mm. For some applications, first axial portion 260 extends to head 240.(The cross section mentioned above with reference to FIGS. 1A-B inanalogous to cross section 264.)

Typically, helical tissue-coupling element 230 has an axial length L2that is at least 3 mm, no more than 20 mm (e.g., no more than 10 mm),and/or between 3 mm and 20 mm, such as 10 mm. Typically, helicaltissue-coupling element 230 is shaped so as to define and radiallysurround an empty space 252 that extends along at least 75% of axiallength L2. In other words, the helical tissue-coupling element typicallyis not shaped so as to define a shank or shaft.

Typically, wire 254 comprises a metal, such as standard implantablealloys known in the art of biomedical implants, such as those describedin ISO 5832 parts 1-14.

For some applications, helical tissue-coupling element 230 has:

-   -   a first axial stiffness along a first axial portion 260 of a        shaftless helical portion 250 of helical tissue-coupling element        230,    -   a second axial stiffness along a second axial portion 262 of        shaftless helical portion 250 of helical tissue-coupling element        230 that is more distal than first axial portion 260), which        second axial stiffness is greater than the first axial        stiffness, and    -   optionally, a third axial stiffness along a third axial portion        264 of shaftless helical portion 250 of helical tissue-coupling        element 30 that is more distal than second axial portion 262),        which third axial stiffness is less than the second axial        stiffness (the third axial stiffness may be equal to or        different from the first axial stiffness).

For some applications, the second axial stiffness is at least 120% ofthe first axial stiffness. For some applications, the first axialstiffness is between 2 and 100 N/mm, and/or the second axial stiffnessis between 3 and 200 N/mm. For some applications, the second axialstiffness is at least 120% of the third axial stiffness. For someapplications, the third axial stiffness is between 2 and 100 N/mm.

These varying axial stiffnesses may be achieved by varying the number oftwists per cm of the length the wire before it is shaped into the helix;axial portions having a greater number of twists per cm are stiffer.Alternatively or additionally, these varying axial stiffnesses may beachieved by varying the thickness of the struts, the chemicalcomposition, and/or by treating the different axial portions, forexample with different thermal treatments along the helix.

For some applications, helical tissue-coupling element 230 has:

-   -   a first axial yield strength along a first axial portion 260 of        a shaftless helical portion 250 of helical tissue-coupling        element 230,    -   a second axial yield strength along a second axial portion 262        of shaftless helical portion 250 of helical tissue-coupling        element 230 that is more distal than first axial portion 260),        which second axial yield strength is greater than the first        axial yield strength, and    -   optionally, a third axial yield strength along a third axial        portion 264 of shaftless helical portion 250 of helical        tissue-coupling element 30 that is more distal than second axial        portion 262), which third axial yield strength is less than the        second axial yield strength (the third axial yield strength may        be equal to or different from the first axial yield strength).

For some applications, the second axial yield strength is at least 120%of the first axial yield strength. For some applications, the firstaxial yield strength is between 5 and 15 N, and/or the second axialyield strength is between 6 and 30 N. For some applications, the secondaxial yield strength is at least 120% of the third axial yield strength.For some applications, the third axial yield strength is between 5 and15 N.

These varying axial yield strengths may be achieved by varying thenumber of twists per cm of the length the wire before it is shaped intothe helix; axial portions having a greater number of twists per cm arestiffer. Alternatively or additionally, these varying axial stiffnessesmay be achieved by varying the thickness of the struts, the chemicalcomposition, and/or by treating the different axial portions, forexample with different thermal treatments along the helix.

One result of these differing axial stiffnesses and/or yield strengthsis that if excessive tension is applied to head 240 at proximal end 242of anchor 220, helical tissue-coupling element 230 generally elongatesalong first axial portion 260 before along second axial portion 262,such that first axial portion 260 serves as a mechanical fuse. Asdescribed hereinabove with reference to FIG. 7C, providing first axialportion 260 effectively reduces the force on the main part of the anchor(e.g., second axial portion 262) which holds the anchor in place,thereby reducing or eliminating the danger of unscrewing the anchor,breaking the anchor, or tearing the tissue, both during the implantationprocedure and thereafter during long-term implantation of the anchor.Alternatively or additionally, the physician may reduce or ceaseincreasing the tension before second axial portion 262 elongates,thereby reducing the risk of the elongation causing damage to the tissuein which second axial portion 262 is implanted, and the risk that thetension will pull the anchor from the tissue. For some applications, thephysician monitors, such as using imaging (e.g., fluoroscopy, computedtomography, echocardiography, sonography, or MRI), the length of firstaxial portion 260 in real time while applying the tension, in order tosense elongation of first axial portion 260. Alternatively oradditionally, the physician may sense the elongation using tactilefeedback. Typically, first axial portion 260 undergoes plasticdeformation when elongated. As a result, excess force applied to theanchor is absorbed by first axial portion 260, instead of detaching theanchor from the tissue, or causing failure elsewhere on the anchor.

For some applications, the axial stiffness of helical tissue-couplingelement 230 varies generally continuously along at least an axialportion of the helical tissue-coupling element, such that helicaltissue-coupling element 230 has (a) the first axial stiffness at only asingle axial location along first axial portion 260, (b) the secondaxial stiffness at only a single axial location along second axialportion 262, and/or (c) the third axial stiffness at only a single axiallocation along third axial portion 264.

Alternatively or additionally, the axial stiffness of helicaltissue-coupling element 230 is constant along one or more axial portionsof the helical tissue-coupling element, such that helicaltissue-coupling element 230 has (a) the first axial stiffness at aplurality of axial locations along first axial portion 260, (b) thesecond axial stiffness at a plurality of axial locations along secondaxial portion 262, and/or (c) the third axial stiffness at a pluralityof axial locations along third axial portion 264.

For some applications, the axial yield strength of helicaltissue-coupling element 230 varies generally continuously along at leastan axial portion of the helical tissue-coupling element, such thathelical tissue-coupling element 230 has (a) the first axial yieldstrength at only a single axial location along first axial portion 260,(b) the second axial yield strength at only a single axial locationalong second axial portion 262, and/or (c) the third axial yieldstrength at only a single axial location along third axial portion 264.

Alternatively or additionally, the axial yield strength of helicaltissue-coupling element 230 is constant along one or more axial portionsof the helical tissue-coupling element, such that helicaltissue-coupling element 230 has (a) the first axial yield strength at aplurality of axial locations along first axial portion 260, (b) thesecond axial yield strength at a plurality of axial locations alongsecond axial portion 262, and/or (c) the third axial yield strength at aplurality of axial locations along third axial portion 264.

Reference is made to FIG. 8C. As mentioned above, the varying axialyield strengths and/or axial stiffnesses of the different axial portionsof helical tissue-coupling element 230 may be achieved by varying thenumber of twists per cm of the length the wire before it is shaped intothe helix. For some applications, first axial portion 260 is not twisted(i.e., has zero twists per cm) in order to provide this axial portionwith its relatively low axial yield strength and/or axial stiffness. Forsome applications, all or a portion of third axial portion 264, e.g.,the tip, is ground smooth.

Reference is now made to FIGS. 9A-B and 10A-B, which are schematicillustrations of two configurations of a delivery system 700, inaccordance with respective applications of the present invention.Delivery system 700 is used to deliver first tissue-engaging element 660a, and be implemented in combination with the techniques describedhereinabove with reference to FIGS. 7A-D. First tissue-engaging element660 a comprises tissue anchor 20, tissue anchor 120, or tissue anchor220, described hereinabove with reference to FIGS. 1A-B, 2A-B, and 8A-C,respectively, or another tissue anchor that is known in the art (whichis optionally inserted by rotation). By way of illustration and notlimitation, in the configuration shown in FIGS. 9A-B and 10A-B, firsttissue-engaging element 660 a comprises tissue anchor 20, describedhereinabove with reference to FIGS. 1A-B. First tissue-engaging element660 a is designated for implantation at least in part in cardiac tissueat first implantation site 630, as described hereinabove with referenceto FIGS. 7A-B.

Delivery system 700 comprises anchor-deployment tube 624, describedhereinabove with reference to FIGS. 7A-D. Delivery system 700 furthercomprises a radiopaque marker 710, which is coupled to a distal end 712of anchor-deployment tube 624, such as by a flexible connecting element,such as a spring 714, as shown in FIGS. 9A-B, a braid 716, as shown inFIGS. 10A-B, a mesh, or a cut tube. Radiopaque marker 710, and theflexible connecting element (spring 714, braid 716, the mesh, or the cuttube) are initially arranged radially surrounding first tissue-engagingelement 660 a, such that radiopaque marker 710 is axially moveable alongfirst tissue-engaging element 660 a with respect to distal end 712. Aninner diameter of radiopaque marker 710 is slightly larger than an outerdiameter of first tissue-engaging element 660 a. The flexible connectingelement (spring 714, braid 716, the mesh, or the cut tube) axiallycompresses as marker 710 moves toward distal end 712. The flexibleconnecting element (spring 714, braid 716, the mesh, or the cut tube)biases the marker distally. Marker 710 may have any appropriate shape,such as a disc.

For applications in which braid 716 is provided, as shown in FIGS.10A-B, the braid comprises biocompatible alloys such as St.St., Co.Cr.,Titanium, NiTi or similar, or stiff polymers such as PEEK, PEKK orsimilar.

For some applications, radiopaque marker 710 is coupled to distal end712 of anchor-deployment tube 624 by both spring 714 and braid 716(configuration not shown). The braid radially surrounds the spring, andhelps ensure that the spring remains straight, rather than bulgingradially outward.

As shown in FIGS. 9A and 10A, as the physician begins to rotate firsttissue-engaging element 660 a into tissue at first implantation site630, spring 714 or braid 716 (or the mesh or the cut tube) pushes marker710 distally against the surface of the tissue. Marker 710 does notpenetrate the tissue, and thus remains at the surface of the tissue, incontact therewith. As a result, as the physician continues to rotateelement 660 a further into the tissue, the surface of the tissue holdsmarker 710 in place, bringing marker 710 closer to distal end 712 ofanchor-deployment tube 624 and closer to head 40 of element 660 a.

Both marker 710 and more proximal portions of the anchor (such as head40) are viewed using imaging (e.g., fluoroscopy, computed tomography,echocardiography, sonography, or MRI), and the distance between themarker and the proximal end of the anchor (e.g., the head) is estimatedand monitored in real time as the anchor is advanced into the tissue.When the marker reaches a desired distance from the head (such asreaches the head itself), the tissue-coupling element has been fullyadvanced, e.g., screwed, into and embedded in the tissue, and thephysician thus ceases rotating the anchor.

Alternatively or additionally, anchor-deployment tube 624 comprises oneor more radiopaque markers near distal end 712 thereof.

The scope of the present invention includes embodiments described in thefollowing applications, which are assigned to the assignee of thepresent application and are incorporated herein by reference. In anembodiment, techniques and apparatus described in one or more of thefollowing applications are combined with techniques and apparatusdescribed herein:

-   -   U.S. application Ser. No. 12/692,061, filed Jan. 22, 2010, which        published as US Patent Application Publication 2011/0184510;    -   International Application PCT/IL2011/000064, filed Jan. 20,        2011, which published as PCT Publication WO 2011/089601;    -   U.S. application Ser. No. 13/188,175, filed Jul. 21, 2011, which        published as US Patent Application Publication 2012/0035712;    -   U.S. application Ser. No. 13/485,145, filed May 31, 2012,        entitled, “Locking concepts,” which published as US Patent        Application Publication 2013/0325115;    -   U.S. application Ser. No. 13/553,081, filed Jul. 19, 2012,        entitled, “Method and apparatus for tricuspid valve repair using        tension,” which published as US Patent Application Publication        2013/0018459; and    -   International Application PCT/IL2012/000282, filed Jul. 19,        2012, entitled, “Method and apparatus for tricuspid valve repair        using tension,” which published as PCT Publication WO        2013/011502.

In particular, the tissue anchors described herein may be used as one ormore of the tissue anchors (e.g., the helical tissue anchors) describedin the above-listed applications, in combination with the othertechniques described therein.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1.-94. (canceled)
 95. Apparatus comprising: a tissue anchor, which (a)comprises a helical tissue-coupling element which has a distaltissue-penetrating tip at a distal end of the tissue anchor, and whichis configured to be advanced into soft tissue, and (b) is shaped so asto define a longitudinal channel extending to the distal end of thehelical tissue-coupling element; and a depth-finding tool, whichcomprises a radiopaque bead that is axially moveable along the channelso as to serve as a marker indicating a depth of penetration of thetissue-coupling element into the soft tissue.
 96. The apparatusaccording to claim 95, wherein the radiopaque bead is positioned withinthe channel.
 97. The apparatus according to claim 95, wherein thelongitudinal channel extends from a proximal end of the anchor to thedistal end of the helical tissue-coupling element.
 98. The apparatusaccording to claim 95, wherein the depth-finding tool further comprisesa shaft that is removably positioned within the channel.
 99. Theapparatus according to claim 95, wherein the radiopaque bead is shapedso as to define a hole therethrough.
 100. The apparatus according toclaim 99, wherein the radiopaque bead is positioned within the channel,wherein the longitudinal channel extends from a proximal end of theanchor to the distal end of the helical tissue-coupling element, andwherein the depth-finding tool further comprises a shaft that isremovably positioned within the channel, such that the shaft passesthrough the hole of the radiopaque bead, and such that the radiopaquebead is axially moveable along the shaft and along the channel.
 101. Theapparatus according to claim 99, wherein the hole of the radiopaque beadis configured to ride over the helical tissue-coupling element, suchthat the radiopaque bead is axially moveable along the channel in ahelical path.
 102. The apparatus according to claim 95, wherein thehelical tissue-coupling element is shaped so as to define a distalstopper that prevents the radiopaque bead from exiting from the distalend of the helical tissue-coupling element.
 103. The apparatus accordingto claim 95, wherein the depth-finding tool further comprises a wire,which is at least partially disposed within the channel, and whichcouples the radiopaque bead to the a proximal portion of the tissueanchor, thereby preventing the radiopaque bead from exiting the distalend of the tissue anchor.
 104. A method comprising: providing a tissueanchor, which (a) includes a helical tissue-coupling element which has adistal tissue-penetrating tip at a distal end of the tissue anchor, and(b) is shaped so as to define a longitudinal channel extending to thedistal end of the helical tissue-coupling element; providing adepth-finding tool, which includes a radiopaque bead that is axiallymoveable along the channel; and advancing the helical tissue-couplingelement into soft tissue, such that the radiopaque bead comes intocontact with and remains at a surface of the soft tissue so as to serveas a marker indicating a depth of penetration of the tissue-couplingelement into the soft tissue.
 105. The method according to claim 104,further comprising: viewing the radiopaque bead and a proximal portionof the soft tissue anchor using imaging; and assessing the depth ofpenetration of the helical tissue-coupling element into the soft tissueby estimating a distance between the radiopaque bead and the proximalportion of the tissue anchor.
 106. The method according to claim 104,wherein the radiopaque bead is positioned within the channel.
 107. Themethod according to claim 104, wherein the longitudinal channel extendsfrom a proximal end of the anchor to the distal end of the helicaltissue-coupling element.
 108. The method according to claim 104, whereinthe depth-finding tool further comprises a shaft that is removablypositioned within the channel.
 109. The method according to claim 108,wherein the radiopaque bead is positioned within the channel, andwherein the method further comprises proximally withdrawing the shaftfrom the channel, leaving the radiopaque bead in the channel.
 110. Themethod according to claim 109, wherein proximally withdrawing the shaftfrom the channel comprises proximally withdrawing the shaft from thechannel after finishing advancing the helical tissue-coupling elementinto the soft tissue.
 111. The method according to claim 108, wherein adistal tip of the shaft is sharp, and wherein the method furthercomprises, before advancing the helical tissue-coupling element into thesoft tissue, inserting the sharp distal tip of the shaft into the softtissue slightly, in order to prevent sliding of the depth-finding tooland the anchor on a surface of the soft tissue before advancing theanchor into the tissue.
 112. The method according to claim 108, whereina distal tip of the shaft is sharp, and wherein the method furthercomprises advancing the shaft into the soft tissue while advancing thehelical tissue-coupling element into the soft tissue.
 113. The methodaccording to claim 104, wherein the radiopaque bead is shaped so as todefine a hole therethrough.
 114. The method according to claim 113,wherein the radiopaque bead is positioned within the channel, whereinthe longitudinal channel extends from a proximal end of the anchor tothe distal end of the helical tissue-coupling element, and wherein thedepth-finding tool further includes a shaft that is removably positionedwithin the channel, such that the shaft passes through the hole of theradiopaque bead, and the radiopaque bead is axially moveable along theshaft and along the channel.
 115. The method according to claim 113,wherein the hole of the radiopaque bead is configured to ride over thehelical tissue-coupling element, such that advancing the helicaltissue-coupling element into the soft tissue causes the radiopaque beadto axially move along the channel in a helical path.
 116. The methodaccording to claim 104, wherein the helical tissue-coupling element isshaped so as to define a distal stopper that prevents the radiopaquebead from exiting from the distal end of the helical tissue-couplingelement.
 117. The method according to claim 104, wherein thedepth-finding tool further includes a wire, which is at least partiallydisposed within the channel, and which couples the radiopaque bead tothe a proximal portion of the tissue anchor, thereby preventing theradiopaque bead from exiting the distal end of the tissue anchor.